Sample Call

<?php
// SOAP_CLIENT_BASEDIR - folder that contains the PHP Toolkit and your WSDL
// $USERNAME - variable that contains your Salesforce.com username (must be in the form of an email)
// $PASSWORD - variable that contains your Salesforce.ocm password

define("SOAP_CLIENT_BASEDIR", "../../soapclient");
require_once (SOAP_CLIENT_BASEDIR.'/SforcePartnerClient.php');
require_once (SOAP_CLIENT_BASEDIR.'/SforceHeaderOptions.php');

try {
  $mySforceConnection = new SforcePartnerClient();
  $mySoapClient = $mySforceConnection->createConnection(SOAP_CLIENT_BASEDIR.'/partner.wsdl.xml');
  $mylogin = $mySforceConnection->login($USERNAME, $PASSWORD);

  $processSubmitRequest1 = new ProcessSubmitRequest();
  $processSubmitRequest1->objectId = "00Q5000000G7YV8";
  $processSubmitRequest1->comments = "Please approve this request.";
  $processSubmitRequest1->nextApproverIds = array("00530000000tH4t");

  $processSubmitRequest2 = new ProcessSubmitRequest();
  $processSubmitRequest2->objectId = "00Q5000000J4pQp";
  $processSubmitRequest2->comments = "Please approve this request.";
  $processSubmitRequest2->nextApproverIds = array("00530000000tH4t");  
  
  $processSubmitRequestResponse = $mySforceConnection->processSubmitRequest(array ($processSubmitRequest1, $processSubmitRequest2));

  print_r($processSubmitRequestResponse);
} catch (Exception $ex) {
  echo $mySforceConnection->getLastRequest();
  print_r($ex);
}
?>

Sample Output

Array
(
    [0] => stdClass Object
        (
            [entityId] =>
            [errors] => stdClass Object
                (
                    [fields] =>
                    [message] => Cannot submit object already in process.
                    [statusCode] => ALREADY_IN_PROCESS
                )

            [instanceId] =>
            [instanceStatus] =>
            [newWorkitemIds] =>
            [success] =>
        )

    [1] => stdClass Object
        (
            [entityId] => 00Q5000000J4pQpEAJ
            [instanceId] => 04g500000004R4BAAU
            [instanceStatus] => Pending
            [newWorkitemIds] => 04i500000004Rp6AAE
            [success] => 1
        )

)