Apps follow the account, not the phone. You have a mobile phone with a 2FA app, the app is saved to your account, if you have to replace your phone your the app will follow when you upload your account data to the new phone.
If you use a phone that doesn't offer back ups of your data, you could be at risk.
Whether google 2fa can be used by two phones simultaneously? Because I've experienced a bootloop that caused the loss of all data on my phone including 2fa googleIf you use a phone that doesn't offer back ups of your data, you could be at risk.
Why would you want to? You'd compromise the integrity of the single point of contact authentication. If you encounter a technical issue you have to load your account data onto a new phone. You don't lose all you application data when it's been saved to the cloud.
This isn't always true. Google Authenticator does NOT BACKUP YOUR KEYS. If you loose your phone and don't have a backup of the private keys or the app's data, your accounts are lost. The only way to get them back is to recover your phone, or hope that the customer service can help unlock the account.
I don't think you understand what I'm suggesting or how 2 factor authentication works.
2FA doesn't interact with your private keys. 2FA provides an additional, always changing password that you must enter at the point of log in. There's only one location where the ever changing password can be retrieved - your phone or other device. If you have an account-based mobile service (not a pre paid phone) then you have the ability to save your phone's applications regularly to the cloud. If your phone dies you upload your account replication from the cloud and "voila" your 2FA authenticator app is back in your hands.
This has nothing to do with private keys or bitcoin.
