There are a lot of reasons for using a good stand-alone camera over the one in your smartphone, but for most people the one they're always carrying that makes images and video easy to post online is adequate. Plus they happen to be getting better. Big improvements coming in the next generation or two. Apple filed patents suggesting a three sensor camera using dichroic mirrors a periscope like optical path in the camera body. They should be able to use a larger lens for low light capability, have better focus control and much better color quality and control with three physically separate sensors. They also bought a company that is going multiple sensor/lens image synthesis which could have separate uses, but would make manufacturing the three sensor camera less expensive. Their competition must be working on similar projects - all of this is sort of obvious next step work.
Results in the hands of professionals are impressive. There have been some wonderful smartphone based still images - much better than I could ever hope to take. The cameras are good enough that they aren’t professionally embarrassing and their lack of flexibility is seen as a plus by some. Recently John Lasseter said that serious film story telling was going to happen on GoPro and iPhones. I would agree, but note the GoPro is really a specialist camera. I doubt it will see much further growth.
Here’s an example of a video Bentley commissioned. They “cheat” and use a steadicam , an accessory lens, and a real microphone but the software is $5 to $10 and you can rent the kit. All you need is the skill:-) There are teens that could pull this off. The really good ones may even graduate to professional tools for greater control and creativity, but the gap to what is good enough continues to shrink.
and how they made the video (it also mentions an earlier one made with a last generation camera)