See the solution in the explanation below:
Explanation
To prevent incoming Teams call notifications when users are already on a Teams call or in a Teams meeting, you can use the Teams admin center to enable the Mute notifications during meetings and calls option. This option will suppress the incoming call notifications without rejecting the call. The caller will still hear the ringing tone and the callee can still answer the call from the Teams app or the taskbar. Here are the steps to enable this option:
Sign in to the Teams admin center with your Microsoft 365 username and password1.
In the left navigation, go to Teams > Teams update policies.
Select an existing policy or create a new one by clicking Add.
In the Update policy pane, under Meetings and calls, turn on the toggle for Mute notifications during meetings and calls.
Click Save and then Close.
Note: You can assign different update policies to different users or groups of users. For more information, see Manage update policies in Microsoft Teams2.

According to the Microsoft documentation1, you need to add an emergency address for each location where your users make and receive phone calls. An emergency address is a civic address-the physical or street address of a place of business for your organization. It is used to route emergency calls to the appropriate dispatch authorities and to assist in locating the emergency caller.
After you add an emergency address, you need to assign a phone number to it. You can assign either a user number or a service number. A user number is assigned to a specific user in your organization who makes and receives phone calls. A service number is used for services such as Audio Conferencing (for dial-in numbers), auto attendants, or call queues.
To assign a phone number to an emergency address, you need to modify the location for each phone number. You can do this by using the Microsoft Teams admin center or PowerShell. For example, to modify the location for a user number by using PowerShell, you can use the Set-CsOnlineVoiceUser cmdlet with the -LocationID parameter2.