You can rent movies in standard (480p) definition from the iTunes Store and watch them on iPhone. You can download rented movies directly to iPhone, or transfer them from iTunes on your computer to iPhone. You can also transfer rented movies back to iTunes from iPhone. (Rented movies aren’t available in all regions.)
The movie must be fully downloaded before you can start watching. You can pause a download and resume it later. Rented movies expire after a certain number of days, and once you start a movie you have a limited amount of time to finish watching it. The time remaining appears near a movie’s title. Movies are automatically deleted when they expire. Check the iTunes Store for the expiration time before renting a movie.
Connect iPhone to your computer. Then select iPhone in the iTunes sidebar, click Movies, and select the rented movies you want to transfer. Your computer must be connected to the Internet.
On iPhone, choose iPod > Videos and select a movie.