Consuming XML SOAP with php

I am relatively new to webservices and so i need help consuming an asmx webservice and the xml for it is as follows.

SOAPAction: "http://www.mywebsite.com/CheckClient"

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<CheckClient xmlns="http://www.ibls.co.za/">
<PolicyNr>string</PolicyNr>
<IDNumber>string</IDNumber>
</CheckClient>
</soap:Body>
</soap:Envelope>

Thanks for your help in advance.