I've shot two short films using smartphones - a horror movie I got a bronze award for using a Nexus 5X, and a personal passion project using a Google Pixel. I intend to shoot the sequel to the passion project later this year using a mix of the Pixel and the Pixel 2 (or whatever it's called.)
Really what clinched it for me was the DJI Osmo Mobile, it came out at the perfect time and is *so* dead-simple to use. I bought a Nebula 4000 a few years ago and it was extremely difficult to use, and just ate up a ton of time calibrating it before each shoot when I was trying to run-and-gun it. The Osmo Mobile in comparison was an absolute dream and I never want to go back to using anything else (save for maybe an improved future model...)
Also it's probably heresy to admit I'm shooting on a non-iPhone, but Filmic Pro's Android version is still great and the Pixel has an objectively fantastic camera. :) Looking forward to the Pixel 2 entirely for the camera improvements (before now, I never bought a new smartphone within two years of my last one.)
Edit- Also my advice to anyone looking to use a smartphone:
1. Always have a second smartphone ready to go at a moment's notice. Overheating and dead bateries are real.
2. Always get the largest capacity storage model you can. (My Pixel is 128 GB. I'd likely get a 256 GB model Pixel 2 if they have it.)
3. Only record in Airplane Mode.
4. Buy Filmic Pro and master it as much as you can.
5. Check out the DJI Osmo Mobile. The DJI app to control it is optional, IMO.
6. Have a large-capacity external battery ready to go at any time.
I backup my footage to an external drive and then to Google Drive. Haven't lost anything yet. *knock on wood.*
I love Frame.io's UI and featureset, and them adding new features this soon after launch bodes very well. Though I wish the "tight integration" was with an NLE people actually use, like Premiere Pro CC. I'm sure they're working on it though. :)