That's what recovery codes are for. On the login screen, click "Lost access to your authenticator app? Use a recovery code" and enter one of the codes you saved — each code works once. Once you're back in, the Security tab of your Account Settings shows how many unused codes you have left and lets you generate a fresh set at any time (generating a new set invalidates the old one). Signing in with a recovery code usually means the device itself is gone, so the best next step is to disable 2FA there and re-enable it on your new phone — that gives you a new secret and a new set of codes. If you've lost your recovery codes too, email
[email protected] from your account's email address and we'll help you regain access.