NuSOAP到PHP SOAP

Question

Currently trying to update some legacy code to use PHP SOAP instead of the old NuSOAP library. The issue I'm having is that the current code has the following:

$parameters = array(
                'request' => array(
                    'UserCredentials' => array(
                        'Username' => $username,
                        'Password' => $password,
                        'AgentID' => $ResellerID,
                    ),
                    'UserConsent' => 'Yes',
                    'ServiceType' => 'MPF',
                )
            );

$parameters['request']['RequestDetails'] = new soapval('RequestDetails', 'TelephonePostcodeRequest', array('TelephoneNumber' => $phone_number, 'Postcode' => $post_code), false, "tns", false);

The problem is that soapval needs to be replaced with what I assume SoapVar() ? I've attempted the following

$parameters['request']['RequestDetails'] = new SoapVar(array('TelephoneNumber' => $phone_number, 'Postcode' => $post_code), XSD_STRING, 'TelephonePostcodeRequest');

with no luck. How can I get a similar object to pass through to the SOAP request?