My phone is not showing nfc

What do you mean "not showing NFC?" There is no setting for NFC on iPhone. It recognizes a NFC reader when it is close to one, like for Apple Pay. For example, if you want to use Apple Pay at a NFC reader, you double tap the side button and the payment method you've set as your default card appears on your screen, after which you place your phone close to the reader and payment is made. This is how NFC was designed to work on iPhone.

If you are asking about something different, please provide more details.

Starting with the iPhone XS, NFC reading is automatic and there is no setting for it. Before that you had the option in the Control Center to activate it.

Mac Jim ID just above, correctly tells you there is no NFC option in Control Center. That was eliminated a while ago as NFC is automatic and there is no need to turn it on or off.

No, I can't tell you how. Whoever you get this door card from, is who you should check with. There are some NFC cards, which just don't work with iPhone unless you have a dedicated app from the manufacturer. Check with them for guidance.

That's correct. If you have a smart lock, you probably need to use an app from the manufacturer to add the card to your wallet. Contact the manufacturer of the lock for support.

Contact the manufacturer of the lock for support.