I just turned on 2fa for CitrusLime and when you click on 'Setup for SMS' the user has to have a number already associated with their account before finalising this.
for larger companies this is no good as the administrator will have to go through, collect numbers and then add numbers for 200+ people, this will take days out of a users time to do this.
to appeal to your larger customers, there needs to be a self service area for the users. we've had to turn off 2fa until we can work out next steps
allowing a user to enter their own number is how any other system works, e.g. Dojo which is a payment provider with super high security