Using passcode of face recognition to unlock phone

You need to setup a passcode in order to user Face ID. You can then decide whether or not you want to setup Face ID (it is optional).

If you do setup Face ID, then you can use either Face ID or the passcode to unlock the phone.

Even if Face ID is set up, you will need to enter the passcode any time that the phone is restarted.

My wife's phone has Face ID but I use her passcode (which sh has given to me) when she wants me to do something with her phone.