You can use the dial pad to call anyone from Teams. Simply click Calls  Calls button on the left side of the app. From there, you’ll see the dial pad and be able to enter a phone number. The person you’re calling doesn’t have to be using Teams.  

To access your dial pad during a call, go to your call controls and select Keypad  Dial pad button .

Note: If you don't see the dial pad, your company may not have purchased a calling plan.