
The steps outlined in this blog will work with regular and external accounts in Azure Active Directory where you are a guest. Have you ever gotten a new phone only to remember that you have to transfer your Microsoft Authenticator information to the new device? It turns out that this is a somewhat complex, poorly documented process. Please remember to " Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.Migrating Microsoft Authenticator on a New Phone or Device

Thank you for your time and patience throughout this issue. If you have any other questions, please let me know. Go to the two-step verification area of either your MyApps page or your organization's custom portal to turn off verification for your old device.

Thank you for your post! Since you don't have access to your old phone and your backup failed, you can try to treat this issue as a "lost phone" scenario.
