If an individual Cisco VoIP phone is exhibiting unexpected behaviour, perform the following steps.
Reboot the device by unplugging the network cable for 5 seconds (the device should lose power), and plugging it back in. The phone will take a minute to restart.
If that doesn't work, try factory resetting the phone by going to
Settings > Admin Settings > Reset Settings > All
If these steps do not resolve the issue, reach out to Compugen.