Dear Fred,
Good day!
Thank you for posting to Microsoft Community. We are happy to assist.
We do understand that you have some queries regarding teams phone system set up. Based on your description, you can set up a teams call queue for the hotline.
In creating the call queue, you have to create a resource account and assign a Phone number to it. This is what the users will call.
In the call queue, you can then assign a user or users to pick up the incoming calls to the queue usually called agents. These should be teams users and the calls that come in will be routed to them via the teams desktop app or mobile app.
When an agent or user receives an incoming call from a call queue, this will indicate that the call is for the queue (call for xxx/showing the call queue resource account name) on the incoming call banner. Example in screenshots below from my test lab on both desktop and mobile.
For more info, please see Create a call queue in Microsoft Teams - Microsoft Teams | Microsoft Learn
Your patience and cooperation are much appreciated. Looking forward to your response.
Sincerely,
Ashraf | Microsoft Community Moderator