We've made some adjustments to the two-factor implementation to now include backup verification codes.
If you have two-factor enabled on your account, you should now see a section under it labeled: "Backup codes"
"Show codes" will show you the currently available and unused backup codes for your account.
"Reset codes" will generate a completely new set of ten backup codes for your account.
Each of these codes may be used once.
These codes exist as a means of getting into your account if you've misplaced or lost your phone with the authenticator application on it. You may use them anywhere an authentication code is expected.
As a side note, the iOS version of the HE Network Tools app will sync HOTP/TOTP credentials in iCloud Keychain, if enabled, and therefore can be an option if you tend to be prone to phone loss/damage/etc.