You need to link your telephone number to use an AirTag indirectly - i.e. You need an AppleID to link the AirTag to, and you are required to provide a telephone

You need to link your telephone number to use an AirTag indirectly - i.e. You need an AppleID to link the AirTag to, and you are required to provide a telephone number in order to create an AppleID (which is validated via SMS). In principle, Apple has the ability to match the AirTag to a phone number (if they do this or not, I don't know).