They are displayed by default when you enable 2FA. If I remember correctly there is a note stating that we should print them out or save in a secure location. They are meant to be used in this exact scenario where you don't have access to the 2FA device registered.

When I was changing phones and wasn't sure that Google Authentication app would move to the new phone seamlessly I actually disabled 2FA on all my accounts before activating the new phone and then set it up again over there. Did I need to do this, probably not but it did ensure that I wouldn't loose access due to a missing 2FA app.