When you first registered your Fire phone with an Amazon account, during the setup process, you enabled your device to share content with other Kindle devices and applications registered to the same account. By default, Whispersync synchronizes your books, audiobooks, personal documents, games, and Amazon Instant Video across all supported devices and applications. Your Fire phone automatically connects to the Cloud Drive after you are connected to the Internet. All content is sorted into its appropriate library on your phone. If you just purchased a book on your Kindle Fire tablet, tap the Sync button in the Quick Actions panel of your Fire phone to sync with your other devices.
Amazon Cloud Drive
Cloud Drive is already built in to your Fire phone and automatically backs up your device settings, notes, bookmarks, call history, installed apps, and more, so you can restore your device without connecting to a computer. As an Amazon Customer, you get 5GB of storage for free. Fire phone users get unlimited storage for full-resolution photos taken on your phone. Cloud Drive also automatically backs up your video as well, but after you reach that 5GB limit, you need to either delete photos from the Cloud to make room for different photos or buy more Cloud space. Amazon will quit uploading your videos but still continue to upload photos. You can find out more about purchasing extra Cloud storage at https://www.amazon.com/clouddrive/learnmore#features-section.