I have not tested this system yet, it interests me a lot because I am faced with a lot of fake accounts that try to defraud others. Now, I wonder, are honest people ready to give their private number to register on a site? I do not know, to think, but I'm glad that this possibility exists.
Otherwise, I think you need to create an account at Twilio and enter your settings in Options -> System -> Security -> Twilio.
Then go to "Options" -> "Accounts" and activate "#2FA" and choose, if you want #activation "#phone", or "phone + Email".

I guess you have to uncheck "Automatic account activation after creation "
This should then work.