As part of the University's move to enable hybrid working patterns, a strategic-level decision has been made: to move away from the Cisco CallManager VoIP system in favour of SIP Phones. These SIP phones are compatible with the ordinary telephone network, just like the CallManager system, but also interact with Microsoft Teams so if you use a Teams client on your mobile you'll be able to make and receive phone calls from that device as well, using your allocated University extension number.
The UIS has further details about the move to Teams Telephony.