Web Services Framework for PHP by WSO2 is by far the most comprehensive stack that provides most WS-* features for a typical PHP Web Services developer, having to put in the least amount of effort to get something done. The comparison of various strategies opted by PHP developers to Web Services is detailed in this post by Samisa.
Meanwhile, the WSF/PHP sphere of possibilities have gone from basic WS through SOAP to most WS-* specifications supported and also the demanding support for RESTful Web Services. Uthaiyashankar, and Katie in this video (story found in here) explains what makes WSF/PHP a well rounded product for your enterprise PHP-based Web Services applications.
Samisa also explains in this post how WSF/PHP blends well into the domain of enterprise-grade WS applications in PHP. This briefs many a feature of WSF/PHP against various expectations of the users of Web Services in PHP.
WSF/PHP's capabilities were appreciated by Andi Gutmans (CTO and Co-Founder of Zend), recently; who explained the mutual collaboration of WSO2 and Zend to make enterprise WS with PHP better as, "Zend and WSO2 are mutually dedicated to serving the diverse needs of PHP developers with world-class open-source software for implementing Web services. By bringing support for both enterprise-oriented WS-* and REST Web services to our managed PHP production environment, WSO2 joins us in empowering the developers supporting more than 20 million PHP websites with unprecedented flexibility for delivering enterprise-class Web services."
I therefore believe that the benefits of using WSF/PHP as a WS enabler in your PHP website or application is clear beyond further justification.