[rstat1]

My MS account does not have a phone number attached to it. Had the same account for over a decade. Never been locked out over it.

I do use the Authenticator app on my phone to login in though.

[OrbitalShotput_]

I suspect the MS Authenticator app is why- the question is then of course, does the app give Microsoft your phone number on it's own once installed?

[ianburrell]

Microsoft account supports TOTP. You don't need to use Microsoft's authenticator app, you can use any that supports TOTP. Google Authenticator is unlikely to send your phone number to Microsoft.

[LWIRVoltage]

Indeed, but some of my test accounts setup using TOTP still have been hit by the phone number prompt, where this poster didn't- so they might treat their own authenticator higher. (And if they do, i have to wonder if it means it sends more data back than others do)