<?php
    require('exacttarget_soap_client.php');
    $wsdl = 'https://webservice.exacttarget.com/etframework.wsdl ';

    try {

        $client = new ExactTargetSoapClient($wsdl, array('trace'=>1));
        $client->username = 'myUsername';
        $client->password = 'myPassword';

        $port = new ExactTarget_Portfolio();
        $port->DisplayName = 'API Uploaded Test v10';
        $port->CustomerKey = 'API Uploaded Test v10';
        $rs = new ExactTarget_ResourceSpecification();
        $rs->URN = 'http://email.exacttarget.com/myFolder/myFile.jpg'; //not sure if this is right
        $port->Source = $rs;
        $port->FileName = 'myFile.jpg'; //file in the same folder as the php file
        $object = new SoapVar($port, SOAP_ENC_OBJECT, 'Portfolio', "http://exacttarget.com/wsdl/partnerAPI ");

        $request = new ExactTarget_CreateRequest();
        $request->Options = NULL;
        $request->Objects = array($object);

        $results = $client->Create($request);
        print_r($results);

    } catch (SoapFault $e) {
        print_r($e);
    }
    ?>

Warning: DOMDocument::loadXML(): xmlns:ns2: 'http://exacttarget.com/wsdl/partnerAPI ' is not a valid URI in Entity

$object = new SoapVar($port, SOAP_ENC_OBJECT, 'Portfolio', "http://exacttarget.com/wsdl/partnerAPI ");

$port->FileName = 'myFile.jpg'; //file in the same folder as the php file