If you need a relatively straightforward cinemagraph app for iPhone and other iOS devices, then consider experimenting with Cinemagraph Pro by Flixel Photos. This app provides tutorials for beginners and professionals on how best to utilize it. The cinemagraph maker from Flixel Photos also avails a gallery full of the best examples of cinemagraphs to get you inspired.
One reason you will love this app is that you can customize every frame you shoot by adding filters. You can also edit your recorded images frame by frame; hence, quite convenient for everyone. Besides, it is easy to get started: upload your video or shoot directly from your device. Select the portion of the footage you want to animate and the section for freezing, and click save.
Though a free version is available, you may not like the giant Flixel logo on your finished product. Get rid of it by paying for a subscription to Flixel Cloud Web + Apps service.