Hello. Let me see if I understand. You’re stuck because every attempt to sign in on the new iPhone sends you to Microsoft Authenticator, and when you try to set up Authenticator on that phone, it asks for a code that only the old device could generate. Do you have access to the other device?
This normally isn’t just an iPhone problem. If you try signing in to your Microsoft account on a computer, does it also ask for an Authenticator approval with no way to move forward?
On the verification screen, there’s usually a link like “Use a different way to sign in” or “I can’t use my Microsoft Authenticator app right now.” If you select that, the system should show any other methods you previously added, such as:
• A one-time code sent to your backup email • A text message sent to your phone number
Do any of those alternative options appear for you? These will only show up if another verification method was set up on the account earlier.