There is basically only two methods to do this:
- Both iPhone would have to be logged in with the same Apple ID. When you pair the AirTag with one phone, it can be tracked with the Find My app on either phone. You do not need to pair it with the second phone.
- If these phones do not share the same Apple ID, then they both have to be running iOS 17.x. You would then set up the AirTag on your device (the one with your Apple ID), and then, you can share it with another person.