I had a need to setup MFA for a large group of users, I have all the users cell phones and I wanted to automate the setup for them. This is the first step in getting MFA setup for the users, then we plan to use the nudge feature to push the usage of Microsoft authenticator.
I found the best way to do this is to use the Microsoft Graph API.
This post from Microsoft docs gives you the PowerShell commands to get started.
I also found this post to be very useful when getting started