If any of the buttons on your Polycom phone are not responding, the complete a "Format File System" procedure through the phone's Home button (which hopefully works).

Press Home/Settings/Advanced/(password 456456)/Admin settings/Reset to Defaults/Format File System.

After the phone reboots, then test the failing buttons.  If the buttons are still failing, then unplug the power from your phone for at least 5 minutes and test again.