2 step verification - what if I trade my cell phone ?? At end of registration it was clear I would my code PLUS the cell phone to get a password reset. What if I change carriers and trade my old phone in ?

At end of registration it was clear I would my code PLUS the cell phone to get a password reset. Something was said about without those two things Apple could NOT reset my account if I forgot my password. What if I change carriers and trade my old phone in ? Am I stuck then ?? That part was confusing.

I started out doing the registration because I wanted to make sure my laptop computer was "registered" - I guess it already was because no opportunity came up for that. But now I'm wondering whether I should have done the two step verification using my cell -- thought I was getting extra security, but now afraid I could be locked out at some point?