diff --git a/app/steps/ui/executors/contactdetails/index.js b/app/steps/ui/executors/contactdetails/index.js
index 49a5920392..daf80db66a 100644
--- a/app/steps/ui/executors/contactdetails/index.js
+++ b/app/steps/ui/executors/contactdetails/index.js
@@ -49,14 +49,13 @@ class ExecutorContactDetails extends ValidationStep {
         if (executorsWrapper.executorEmailAlreadyUsed(ctx.email, executor.fullName, formdata.applicantEmail)) {
             errors.push(FieldError('email', 'duplicate', this.resourcePath, this.generateContent({}, {}, session.language), session.language));
         }
-        if (!PhoneNumberValidator.validateMobilePhoneNumber(ctx.mobile)) {
-            errors.push(FieldError('mobile', 'invalid', this.resourcePath, this.generateContent({}, {}, session.language), session.language));
+        const validationResult = PhoneNumberValidator.validateMobilePhoneNumber(ctx.mobile);
+        if (!validationResult.isValid) {
+            errors.push(FieldError('mobile', validationResult.errorType, this.resourcePath, this.generateContent({}, {}, session.language), session.language));
         }
-
         if (executorsWrapper.executorPhoneNumberAlreadyUsed(ctx.mobile, executor.fullName, formdata.applicant.phoneNumber)) {
             errors.push(FieldError('mobile', 'duplicate', this.resourcePath, this.generateContent({}, {}, session.language), session.language));
         }
-
         if (ctx.email !== executor.email && (executor.emailSent || executor.inviteId)) {
             executor.emailChanged = true;
         }
diff --git a/app/steps/ui/executors/contactdetails/schema.json b/app/steps/ui/executors/contactdetails/schema.json
index b9952d0f3b..1fd1094fc3 100644
--- a/app/steps/ui/executors/contactdetails/schema.json
+++ b/app/steps/ui/executors/contactdetails/schema.json
@@ -11,7 +11,7 @@
     "mobile": {
       "type": "string",
       "minLength": 11,
-      "maxLength": 13
+      "maxLength": 16
     }
   },
   "required": [
diff --git a/app/utils/PhoneNumberValidator.js b/app/utils/PhoneNumberValidator.js
index e31431db58..4bc2a1c380 100644
--- a/app/utils/PhoneNumberValidator.js
+++ b/app/utils/PhoneNumberValidator.js
@@ -1,29 +1,16 @@
-class PhoneNumberValidator {
-    static validateMobilePhoneNumber(num) {
-        const ukNumberMatchRE = new RegExp(/^7[0-9]{9}$/);
-        const ukPrefix = '44';
-        const internationalMatchRE = new RegExp(/^[0-9]*$/);
-
-        if (num.startsWith('+')) {
-            let toValidate = num.slice(1);
-            if (toValidate.startsWith(ukPrefix)) {
-                toValidate = toValidate.slice(2);
-                if (toValidate.match(ukNumberMatchRE)) {
-                    return true;
-                }
-            } else if (toValidate.match(internationalMatchRE)) {
-                return true;
-            }
-        }
+const parsePhoneNumber = require('libphonenumber-js/mobile').parsePhoneNumber;
 
-        if (num.startsWith('07')) {
-            const toValidate = num.slice(1);
-            if (toValidate.match(ukNumberMatchRE)) {
-                return true;
+class PhoneNumberValidator {
+    static validateMobilePhoneNumber(phoneNumber) {
+        try {
+            const parsedPhoneNumber = parsePhoneNumber(phoneNumber, 'GB');
+            if (parsedPhoneNumber && parsedPhoneNumber.isValid()) {
+                return {isValid: true};
             }
+            return {isValid: false, errorType: 'invalid'};
+        } catch (error) {
+            return {isValid: false, errorType: 'invalid'};
         }
-
-        return false;
     }
 }
 
diff --git a/package.json b/package.json
index f18e08eb4c..fc710f5932 100644
--- a/package.json
+++ b/package.json
@@ -129,6 +129,7 @@
     "js-yaml": "^4.0.0",
     "jsdom": "^26.0.0",
     "launchdarkly-node-server-sdk": "^7.0.0",
+    "libphonenumber-js": "^1.11.17",
     "lodash": "^4.17.21",
     "mocha-lcov-reporter": "^1.3.0",
     "moment": "^2.29.4",
diff --git a/test/unit/utils/testPhoneNumberValidator.js b/test/unit/utils/testPhoneNumberValidator.js
index 3beaafcfd4..37367efeb3 100644
--- a/test/unit/utils/testPhoneNumberValidator.js
+++ b/test/unit/utils/testPhoneNumberValidator.js
@@ -3,61 +3,147 @@ const expect = require('chai').expect;
 
 describe('PhoneNumberValidator.js', () => {
     describe('validateUKMobilePhoneNumber()', () => {
-        it('should return failure for invalid number', (done) => {
-            const phoneNumber = '0208 863 8689';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(false);
-            done();
+        describe('Base Case', () => {
+            it('should return true to validate number for testing purposes', (done) => {
+                const phoneNumber = '07123456789';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
         });
-        it('should return failure for invalid chars', (done) => {
-            const phoneNumber = 'abcdef';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(false);
-            done();
-        });
-        it('should return failure for invalid spces', (done) => {
-            const phoneNumber = ' 07958995330';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(false);
-            done();
-        });
-        it('should return failure for uk landline number', (done) => {
-            const phoneNumber = '02088638689';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(false);
-            done();
-        });
-        it('should return fail for uk mobile number INTL staring with 00', (done) => {
-            const phoneNumber = '00447958995330';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(false);
-            done();
-        });
-        it('should return failure for bad format uk mobile number', (done) => {
-            const phoneNumber = '+44 7958995330';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(false);
-            done();
-        });
-        it('should return failure for invalid uk mobile number', (done) => {
-            const phoneNumber = '08958995330';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(false);
-            done();
-        });
-        it('should return pass for uk mobile number INTL', (done) => {
-            const phoneNumber = '+447958995330';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(true);
-            done();
-        });
-        it('should return pass for overseas mobile number', (done) => {
-            const phoneNumber = '+337958995330';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(true);
-            done();
+
+        describe('Length Validation', () => {
+            it('should return false for not meeting minimum length', (done) => {
+                const phoneNumber = '020 1234';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
+            it('should return false for exceeding maximum length', (done) => {
+                const phoneNumber = '020 12345 6789 10 11';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
+            it('should return true for acceptable length (11 chars)', (done) => {
+                const phoneNumber = '07123456789';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return true for acceptable length (15 chars)', (done) => {
+                const phoneNumber = '+4917642010039';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return false for invalid mobile number', (done) => {
+                const phoneNumber = '+179589953302345234';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
         });
-        it('should return pass for uk mobile number', (done) => {
-            const phoneNumber = '07958995330';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(true);
-            done();
+
+        describe('Alphanumeric Input Validation', () => {
+            it('should return false for invalid input', (done) => {
+                const phoneNumber = 'INVALID_INPUT';
+                const validationResult = PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber);
+                const expectedResult = {'isValid': false, 'errorType': 'invalid'};
+                expect(validationResult).to.deep.equal(expectedResult);
+                done();
+            });
+            it('should return true for hyphens input', (done) => {
+                const phoneNumber = '07-1234-56789';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return true for spaces input', (done) => {
+                const phoneNumber = '07 1234 56789';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return false for invalid chars', (done) => {
+                const phoneNumber = 'abcdef';
+                const validationResult = PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber);
+                const expectedResult = {'isValid': false, 'errorType': 'invalid'};
+                expect(validationResult).to.deep.equal(expectedResult);
+                done();
+            });
         });
-        it('should return pass for international mobile number', (done) => {
-            const phoneNumber = '+179589953302345234';
-            expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.equal(true);
-            done();
+
+        describe('International Number Validation', () => {
+            it('should return true for international number (French)', (done) => {
+                const phoneNumber = '+33 6 12 34 56 78';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return true for overseas mobile number', (done) => {
+                const phoneNumber = '+33 7 58 99 53 30';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return true for British with country code', (done) => {
+                const phoneNumber = '+44 7911 123456';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return false for invalid country code', (done) => {
+                const phoneNumber = '+999 6 12 34 56 78';
+                const validationResult = PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber);
+                const expectedResult = {'isValid': false, 'errorType': 'invalid'};
+                expect(validationResult).to.deep.equal(expectedResult);
+                done();
+            });
+            it('should return false for missing country code', (done) => {
+                const phoneNumber = '+ 6 12 34 56 78';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
+            it('should return false invalid international number', (done) => {
+                const phoneNumber = '+44-7911-12345';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
         });
 
+        describe('General Validation Tests', () => {
+            it('should return false for invalid number', (done) => {
+                const phoneNumber = '0208 863 8689';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
+            it('should return false for uk landline number', (done) => {
+                const phoneNumber = '02088638689';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
+            it('should return false for invalid uk mobile number', (done) => {
+                const phoneNumber = '08958995330';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: false, errorType: 'invalid'});
+                done();
+            });
+            it('should return true for uk mobile number INTL', (done) => {
+                const phoneNumber = '+447958995330';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return true for uk mobile number', (done) => {
+                const phoneNumber = '07958995330';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            //The following are edited tests which failed under previous validation
+            it('should return true for spaces', (done) => {
+                const phoneNumber = ' 07958995330    ';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return true for uk mobile number INTL staring with 00', (done) => {
+                const phoneNumber = '00447958995330';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+            it('should return true for spaced format uk mobile number', (done) => {
+                const phoneNumber = '+44 7958995330';
+                expect(PhoneNumberValidator.validateMobilePhoneNumber(phoneNumber)).to.deep.equal({isValid: true});
+                done();
+            });
+
+        });
     });
 });
diff --git a/yarn.lock b/yarn.lock
index 6eeb27e1f8..efd2539ea2 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -10340,6 +10340,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"libphonenumber-js@npm:^1.11.17":
+  version: 1.11.17
+  resolution: "libphonenumber-js@npm:1.11.17"
+  checksum: 10/e8e897834822060fe3067fc573a76f94eb0fbcc1ac075e3fdd9e1870b0c68f7c20f2bc50053ceeb69364fc3a8b881395bd121d904c38f716c4b69c3382b8f011
+  languageName: node
+  linkType: hard
+
 "lie@npm:~3.3.0":
   version: 3.3.0
   resolution: "lie@npm:3.3.0"
@@ -13489,6 +13496,7 @@ __metadata:
     js-yaml: "npm:^4.0.0"
     jsdom: "npm:^26.0.0"
     launchdarkly-node-server-sdk: "npm:^7.0.0"
+    libphonenumber-js: "npm:^1.11.17"
     lodash: "npm:^4.17.21"
     mocha: "npm:^11.0.0"
     mocha-jenkins-reporter: "npm:^0.4.8"