Tap your profile picture, go to Settings, and then tap Calls.
Scroll to PLACE CALLS USING and then choose an option:
Webex Teams | Make Work Calls Over a Mobile Phone Connection
If your administrator has set you up with Dial-via-Office (DvO), you can choose how calls happen in Webex Teams depending on your environment. You have the option to make work calls using your mobile phone connection, which ensures your calls are uninterrupted even if data is unavailable. No matter what option you choose, your work number is always used as the caller ID so people can easily identify you.