If you have 2FA enabled on exchanges and you lose your phone - life is a lot easier with the account key in your posession. Once you scan the QR code and enable 2FA you don't get access to the key again so back it up (write it down) before enabling 2FA.
If you've already enabled 2FA and you don't have the keys...disable 2FA in your exchange account and log out. Log back in to make sure 2FA has been removed, only then remove that sites account from your phone and re-enable 2FA taking note of the key this time.

(Not mine, just a pic from google)
If you've already enabled 2FA and you don't have the keys...disable 2FA in your exchange account and log out. Log back in to make sure 2FA has been removed, only then remove that sites account from your phone and re-enable 2FA taking note of the key this time.

(Not mine, just a pic from google)
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