Teams Free does not have the capabilities to make phone calls. This feature is only available in with Teams Business account and additional phone licences.
However, if you still have some remaining Skype credit or an active Skype calling subscription then you can make phone calls using the Skype Dial Pad site on the Web:
https://calling.web.skype.com/
Just be sure to sign in to this site with exactly the same account as you have used with Skype.