People who have spent money on iPhones have more than enough tech power to do most types of video. The camera and video quality of iPhones are very good. However, all phones need and external microphone for good audio.
I don't have an iPhone because I can't bring myself to spend nearly $1,000 on a phone despite the fact it has superior camera & video qualities.
But since you have one, I would go use it unless you want to spend even more money on DSLR cameras and all that it entails.