Usage by example: Accounting\Contact

Create a contact

$contact = new \XeroPHP\Models\Accounting\Contact();
$contact
    ->setContactNumber($user_id)
    ->setFirstName($detail['fname'])
    ->setLastName($detail['lname'])
    ->setEmailAddress($detail['email'])
    ->setTaxNumber($detail['business_no'])
    ->addAddress(
        (new Address())
            ->setAddressLine1($detail['address'])
            ->setCity($detail['city'])
            ->setRegion($detail['state'])
            ->setPostalCode($detail['postcode'])
            ->setCountry($detail['country'])
    )->addPhone(
        (new Phone())
            ->setPhoneType(Phone::PHONE_TYPE_DEFAULT)
            ->setPhoneNumber($detail['phone'])
    )->addPhone(
        (new Phone())
            ->setPhoneType(Phone::PHONE_TYPE_MOBILE)
            ->setPhoneNumber($detail['mobile'])
    )->setName($ContactName);

$contact->setApplication($app);

$contact->save();

Note: ContactName is unique across the whole application, although Xero suggested not to use it as identifier. Having duplicated ContactName will get you error.