It’s readily solvable not to require a phone number to add a TOTP app.
Phone numbers are nice because the marginal cost to a customer is low (they probably already have one) while the marginal cost to a bad actor is high (it's expensive to acquire many of them or to change one once it's been identified as malicious).
My current twitch subscriptions: 11.97€/month
I can’t really see how they need my phone number to make it too expensive to be a bot.
And if that is the thing, then that’d makes them even more shady, claiming it’s for account security when it’s for their bit protection.