You shouldn’t use a phone number for 2fa to begin with, you’d be better off without 2fa if that’s the only option IMO (assuming you’re using a strong unique password). This is just more fuel on that fire.
In general, SMS is better than no 2FA, but it's weaker than OTP/OTH or a token like YubiKey or Titan.
And IIRC at the time Twitter didn't offer any other 2FA mechanisms.