I know that generally speaking, this cant be done, that is get another PC to call a site hosted under the ASP.NET DEvelopment Web Server remotely (generally
You might want to take a look at UltiDev's version of the Cassini web server. They took the Microsoft Open Source Cassini web server and enhanced it to allow among other things, remote connections.
You can attach VS to the process, and watch your RESTful APIs being called from the PHP application, exactly as you describe above.