If you need to reset the Gradwell Phone application, you can do this from the settings menu. Please note that this will remove all settings and call history.
From the keypad screen, select the three dots in the lower right corner...
and then the Settings link.
From the settings menu, select Reset Application.
To reconfigure the application, please go through the initial configuration instructions (including adding your mobile phone number to the extension, even if you're using the same one as before).