iPhones are pretty capable 4k cameras these days. With a microphone and decent LED light, you can produce professional quality video on them. The SMALLRIG Universal Smartphone Video Rig can help. It has a spring-loaded design to grip phones from 63mm to 86mm. The cage comes with 1/4″-20 threaded holes and two cold shoe mounts for attaching your gear.
The CPU2391 rig has an aluminum alloy and carbon fiber construction with built-in rubber pads on the bottom to prevent scratching. It has an ergonomic design and lets you capture smoother video or simply use your phone as a monitor.[where to get it]