I forgot the password and cannot access the web interface

Your phone has two passwords, administrative and http. If you lose http but still have administrative you can fix this through the web interface as your are trying. If both are lost then you will have to reset the phone to factory defaults by using TFTP to update the frimware. Note that this will result in you starting from scratch with your configuration.

Here is the SNOM wiki article containing directions for doing this:

http://kb.snom.com/kb/index.php?View=entry&CategoryID=44&EntryID=32