Check out https://github.com/econea/nusoap for a PHP 5.4, 5.5, 5.6, 7.0, 7.1 and Composer compatible fork.

NuSOAP is a rewrite of SOAPx4, provided by NuSphere and Dietrich Ayala.
It is a set of PHP classes - no PHP extensions required - that allow developers to create and consume web services based on SOAP 1.1, WSDL 1.1 and HTTP 1.0/1.1.

Here we are maintaining a version that is compatible with PHP 5.3.
All the API's remain unchanged so this code is backward compatible with previous NuSOAP versions.