iPhone 16 not making notification sound when locked

GigglePiggy wrote:

No, that was not me. Yes I do have an Apple Watch. The watch and other related devices like my iPad register and sound the notification but the phone, while locked, does not.

Then you don't have a problem. Your iPhone is doing exactly what it was designed to do. When your phone is locked and you have your watch on your wrist, notifications will be delivered to your watch, NOT your phone. If your phone is unlocked, notifications will be delivered to your iPhone. This is by design and not something you can change or something which needs to be fixed.

See the statement in this support article, which tells you notifications will be delivered to your watch or your phone, but not to both --> Notifications on your Apple Watch - Apple Support

Put your watch on it's charger and see if things change

Did you post this a couple days ago as well? The wording seems remarkably the same. In that thread, I asked if the user wears Apple Watch, but they never came back and responded. So I'll ask you if you wear Apple Watch?