If any of the buttons on your Polycom phone are not responding, complete a “Format File System” procedure through the phone’s Home button (which hopefully works).
Press Home/Settings/Advanced/(456)*/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.
*The default Polycom passcode is 456, however, that code may be different.