iPhone 11 calls specific contacts via Teams instead of making a regular phone call via the Phone app

An employees' iPhone 11 calls specific contacts via Teams instead of making a regular phone call via the Phone app - from the Phone app's contacts list. He's on the latest iOS release - 16.5.1. When this happens, because we don't have any Teams Phone licenses, he sees this message: >**Couldn't complete the call** >This type of call isn't supported on your calling license. >Talk to your IT admin. >[OK] But why does it call specific numbers via Teams anyway? The numbers are all formatted the same 07xxx xxxxxx, and are labelled Mobile. Apart from the numbers and names being different, there doesn't seem to be anything setup differently on the contacts that call via the Phone app and those that switch to Teams when you try calling them. Very odd!! Anyone else seen this and/or found a solution? It's got me stumped!