Use iCloud Photos on iPhone
iCloud Photos automatically uploads the photos and videos you take and stores them in their original format at full resolution. You can access your photos and videos in iCloud Photos from any device where you’re signed in using the same Apple ID.
To use iCloud Photos, you need a device with iOS 8.1 or later, a Mac with OS X 10.10.3 or later, or a PC with iCloud for Windows 5 or later.
Turn on iCloud Photos
Go to Settings > [your name] > iCloud > Photos, then turn on iCloud Photos.
Save space on your iPhone
iCloud Photos keeps all your photos and videos in their original, high-resolution version. You can optimize storage to save space on your iPhone.
Go to Settings > [your name] > iCloud > Photos, then tap Optimize iPhone Storage.
Download a full-resolution photo
If Optimize Storage is on, you can download the full-resolution photo or video by selecting it and pinching in to zoom to 100%. The full-resolution photo or video downloads automatically.
Upgrade your iCloud storage to store more photos
If your uploaded photos and videos exceed your storage plan, you can upgrade your iCloud storage.
Go to Settings > [your name] > iCloud, tap Manage Storage, then tap Upgrade.