I use a fancy Sony mirrorless camera for photography that is meant to be kept and looked at in the future. However, it is pretty obvious why cameras on phones are necessary even to people with good cameras: when communicating with people over a messenger app like Signal or Whatsapp, one quite often has to send them a quick pic to get their opinion. (For example, today I didn't know which kind of olive oil my partner wanted me to pick up from the supermarket, so I just sent a picture of what was available on the shelf.)
Sure, I could have lugged my full-size camera along and then sent it over to the phone via wi-fi, but using a real camera in a supermarket is going to get you some unpleasant attention from staff.
Sure, I could have lugged my full-size camera along and then sent it over to the phone via wi-fi, but using a real camera in a supermarket is going to get you some unpleasant attention from staff.