If you watch the video, you can see that they have a big rig with like a gimbal and external controllers and screens. So it's not "just an iPhone" but it's also not a $50k+ pro camera body.
I think a lot use separate apps. I had a gimbal that I used to use with an old iPhone with buttons to move the gimbal and direct the phone, but also with buttons to start/stop recording, and do other things without touching the phone itself. This gimbal was in the $300-$500 range.