Backup codes are generally used for occasions when you lose your phone, or can not
receive authentication codes by any other means.
Choose whether to
receive authentication codes via text message or via an authenticator app.
You can use this number to
receive an authentication code if you ever lose access to the Google Authenticator app or reformat your device.
Not exact matches
This would be some kind of «who you are» (biometric) or «what you have» (token, phone to
receive code) method of
authentication, rather than a «what you know» password.
You might
receive that
code as a text message, or through an
authentication app on your phone like Google Authenticator or Authy.