Let users add people by phone to meetings
This feature is currently supported from specific countries for calls to the U.S. and Canada using a web browser on your computer. Calls to other countries are not yet supported.
To allow video-meeting participants to add people by phone in Hangouts Meet, you need to turn on Google Voice in the Google Admin console.
Turn on Google Voice
Google Voice is an additional service and isn't subject to the terms of your G Suite account agreement. For details on how to turn it on, see Turn Google Voice on or off.