I am working with action script 3 and often I see server calls that link to php files.
var serverCall:ServerCall = new ServerCall("getDeviceFirmwareLog", getDeviceFirmwareLogResponse, getDeviceFirmwareLogResponse, false);
Without intimate knowledge of your environment, I'd say it appears
ServerCall is a custom socket class that calls external functions, with
n number of arguments.
getDeviceFirmwareLog would therefore be the function being called, and would be a native function to the API of the hardware (not PHP); this is why you wouldn't be able to find it with a grep search.
Consequently, unless it's rigged with event listeners,
ServerCall would populate with the requested data asynchronously (which would likely still fire an event when the request completed).
As you're working with both Flash and PHP, it appears as though you might be testing this through a browser. If so, you could always try the native debugging tools in your browser (
The PHP portion is harder as it's server side scripting, however, take a look at the Eclipse Plugin PDT, which offers debugging facilities for PHP code.