I think mail confirmation or yubikey is fine but I never understood why I need an app on my phone for authentication. What if I lose the phone? How would I get

I think mail confirmation or yubikey is fine but I never understood why I need an app on my phone for authentication. What if I lose the phone? How would I get my account back? Tried some authenticator app on the desktop once also and got locked out of my account after that because my computer crashed and I had to reinstall it. Never again.