If you are looking to shoot a film on your phone because of the access and natural feel it provides, having too many people on set will ruin the entire experience. Get a hold on the minimum number of people required for the project right at the start and stick to that.
Just because you are shooting on a phone doesn't mean that you go all out with a 5-camera set up! The idea is to keep the budget in check. We shot Zoo using just one iPhone for the entire duration. That's all I could afford!
It's very crucial to get the right director of photography. If your cinematographer is not fully convinced about being able to shoot on a phone, the result will not translate on screen.
While we did not use external lenses to shoot Zoo, we did use a stabilizer or a gimbal that helped to keep the frame steady.
It's important to identify why you want to shoot your film on a phone. I extensively researched Tangerine the only other film that has been shot on a phone, analyzed the quality of the footage and then decided to make my movie. Don't do it on a whim.