I actually wasn't aware that it was more than just phone-based since I have never heard of the others! (or at least never heard stuff like that called it, I've gotten emails about "signing in from another device, please verify your account" things before).

I just worry because I don't have a phone at all haha :) And other sites I've been on are pushing the "you should attach a phone number to your account" thing, though it's not required.