The contacts API contains a series of URI endpoints that may be called from any language. For instance, in PHP 5 you may make an OAuth signed request to the endpoints to capture the data. If you're looking for an implementation SDK I would take a look at our PHP SDK: http://developer.yahoo.com/social/sdk/
If there's something specific which you are trying to do, or the exact error that you are seeing on your server, please let us know and we'll do what we can to help.
Jonathan LeBlanc Senior Software Engineer Yahoo! Developer Network Twitter: jcleblanc