This article explains how to watch movies on an iPhone. The information applies to all iPhones and iPads.
iPhone comes with the Apple TV app. You can copy movies and TV shows from your computer to iPhone by syncing your devices in iTunes, or you can download them directly to your phone:
Open the Apple TV app.
Tap Watch Now or Originals at the bottom of the screen to watch a movie. Or tap the search icon to find a specific title.