How are my photos saved in iCloud?

See the articles Use iCloud Photos on iPhone - Apple Support

Access and view iCloud Photos on your iPhone, iPad, or iPod touch - Apple Support

How are you using iCloud for your photos?

If you are using iCloud Photos on your iPhone, iCloud will upload all photos and videos from your iCloud Photos Library in the full resolution, as the central storage of the photos, and then keep this central storage in sync with all devices where you are using iCloud Photos too. Any editing you are doing on one device, any item you delete from Photos or import to Photos will sync to iCloud and update the central iCloud Photos library. From there the changes will sync back to your other devices. The Photos Library will be kept identical across your devices. essentially you will have the central iCloud Photos Library, but with shadow copies on all devices, so you can browse your photos and work with them, even if a device is currently off-line. because of the instant syncing the iCloud Photos Library should be considered to be the only copy of your library, as it will be identical everywhere and change everywhere, when you are working with it. It does not suffice as a backup. as any mistake you make on one device will damage all copies on devices and in iCloud. You need to make regular backup copies of the items in iCloud Photos on a computer.