Creating a WSDL file first, then the service, is doing contract-first development. With Eclipse, PDT, and WST, you have the tools you need to create the WSDL visually and easily, then use Eclipse's features to automatically publish your PHP service to a location.
The PDT project gives you the ability to write PHP code with first-class IDE features. Using the PHP perspective, you can navigate your PHP project more easily. With these tools and the built-in support in PHP for SOAP and XML, you can create PHP Web services with little effort.