I have that setup currently. I needed a phone number initially but could remove it after setting up authenticator.

I'm pretty sure you can remove your number after setting up 2FA.

I just removed my phone number, actually, after seeing news of these hacks. Seems to work fine, I guess if you already have Authenticator set up.

This seems to have changed recently. You can now remove the phone as soon as you add authenticator as an option.