QNAP says there is a "/Web" folder, probably you have to activate their web server first -- see
http://web.qnap.com/pro_application.asp?ap_id=432 for some screenshots
Here are more tutorials for PHP on QNAP:
http://web.qnap.com/pro_features.asp
Unfortunately I don't have a QNAP, so that is only my guess.
Rainer