A Microsoft app for iOS and Android devices that enables authentication with two-factor verification, phone sign-in, and code generation
If your old phone is dead and you cannot access the Microsoft Authenticator app, you may lose the configurations stored within the app unless you had previously set up a recovery option. If you had enabled iCloud backup for the Microsoft Authenticator app on your old device, you might be able to restore your account credentials on your new phone by signing in with the same Microsoft account and restoring from the backup.
However, if you did not set up any recovery options or backups, you will need to reconfigure your accounts manually on the new device. This means you would have to go through the process of setting up multi-factor authentication (MFA) again for each account that was linked to the Authenticator app.
For future reference, it's advisable to enable backup options and recovery settings in the Microsoft Authenticator app to avoid losing access in similar situations.