Common Area phone can be added/ configured through the Admin Portal according the KB. Following are the steps described:
Log in to your RingCentral online account > Go to Phone System > Phones & Devices > Click on Common Area Phones > Click add device
Unfortunately we can't see Common Area Phones entry when we log in to our online account. We only have access to User phones and Unassigned. Is there some prerequisite required to be able to access Common Area Phone functionality?