If you have an A5 license, then you can provide a dial-in number for your Teams meetings. This allows participants to join you by phone when they have limited internet access, or when phone access is otherwise preferred. 

The dial-in number is automatically added to any future meetings you schedule. Attendees do not need a license to join a meeting using the dial-in numbers.

For instructions about using audio conferencing, refer to Microsoft’s documentation at Join a Teams meeting by phone.