Can an iPhone 7 be made to function as a NFC Tag? From what I’ve read, I know the iPhone 7 can work as a NFC reader, but I want it to be a NFC Tag. I have a NFC reader (an ID-12 RFID reader) for my house that controls a door. I’d like to be able to put my iPhone up to it and have the NFC reader on my door read my iPhone's Tag and open.

Can an iPhone 7 be made to function an a NFC tag for a regular external NFC/RFID reader?
The iPhone is perfectly capable of this, but this is a privilege Apple keeps to themselves.

If you're jailbroken, you can install NFCWriter X and do pretty much everything you've asked for. I haven't personally checked, but I would strongly assume this is the exact same way Apple Pay works as well. So the iPhone is certainly capable of this.

The problem is that apps are not capable of this, because Apple denies them the availability of such an API. The CoreNFC framework only allows reading, and the story has gone so far as that organizations have sought fully third-party access to the iPhone's NFC chip on a legal basis. They were dismissed however, with Apple Pay keeping its uniquely privileged status.