Re: Photos in iCloud
iCloud pushes all your photos to the My Photo Stream album on your devices and computers, and manages them efficiently, so you don’t run out of storage space.
Originally Posted by Chris Cook5
Your iOS devices keep a rolling collection of your last 1000 photos in the My Photo Stream album. From there, you can browse your recent photos or move the ones you like to your Camera Roll or another album to keep them on your device forever.
The photos you upload to My Photo Stream are stored in iCloud for 30 days to give your devices plenty of time to connect and download them.
Here's Apple's support knowledge base article on the iCloud photo stream.