How I can check my iCloud photos
How I can see my iCloud photos and data
iPhone 6, iOS 12
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If you have iCloud Photos turned on, the photos on the device are the same as on iCloud, with the possible exception that some of them may be space-saving optimized versions if you have that option turned on. You view them in the Photos app on an iOS device. You can also login to icloud.com and go to the Photos app there. See: https://support.apple.com/en-us/HT204264
If you didn't have iCloud Photos turned on but do have an iCloud backup, you can restore the entire phone (not just the photos) from iCloud but you cannot otherwise view the contents of the backup. https://support.apple.com/kb/ph12521
On an iPhone, iCloud is designed to be viewed by using the apps on the device (e.g., the Files app for iCloud Drive, the Photos app for iCloud Photos, the Notes app for notes, etc.).
You can also use an internet browser and log into icloud.com. What you can access via a browser varies by device. See: https://support.apple.com/en-us/HT210402
Also note that while you can view synced data as described above, it is not possible to view the contents of an iCloud Backup. You can only use the backup to do a full restore of a device or to setup a new device.
The following may also help: https://support.apple.com/en-us/HT204247