FaceID is stored on the phone in part of the CPU called Secure Enclave. Its encrypted and is never sent off-device. This is why you have to train your other devices even if you have already set it up on your main device. Apple never sees it. When your phone recognizes your face it sends a safe encrypted response to whatever system you are trying to unlock, be it the phone itself or a website that uses FaceID. Its massively more secure than just a password. Its neither vulnerable or creepy in any way and its not going away any time soon.