Is there a PHP Sandbox, something like JSFiddle is to JS?
If you are just looking for an online site to play around with PHP code, try
The most sophisticated is:
It lets you test your code in all PHP versions starting from PHP4.
If you want something for your local environment, the Runkit extension aims to provide a PHP Sandbox:
Instantiating the Runkit_Sandbox class creates a new thread with its own scope and program stack. Using a set of options passed to the constructor, this environment may be restricted to a subset of what the primary interpreter can do and provide a safer environment for executing user supplied code.
If you dont want to use Runkit but still want a PHP Console on your server, try