Can I use 1 air tag on 2 phones?

AirTags are linked to AppleIDs … not specific devices.

So IF the 2x iPhones are on the same AppleID … “Yes”

Otherwise … “No”

Note that changes to this architecture are coming in iOS 17 this fall. See more below:

iOS 17 makes iPhone more personal and intuitive - Apple

AirTags are tied to one Apple ID on iOS 16 and earlier.

Whatever mix of iPhone and iPad you have associated with that same Apple ID will all work.

If you have one AirTag you want to use with two Apple IDs as I’d suspect, you will have to wait for iOS 17.

Here is where Apple discusses AirTags and multiple Apple IDs on iOS 17: iOS 17 Preview - Apple