You can choose either Remove from iPhone or Download Photos & Videos, but no matter what you choose, the iCloud originals will remain intact.
If you use iCloud Photos, and delete photos and videos from one device, the photos and videos will be deleted on your other devices. If you add photos to your iPhone or iPad by connecting your device to your computer, you can't delete them directly from your device in the Photos app.
Your content won't be deleted from iCloud when you erase your device.
If you delete photos on iPhone, they are also deleted from iCloud photos library and other devices using the same Apple ID. But you can check the Recently Deleted album on your iPhone or in iCloud photos library. If the deleted photos are there, you can recover them easily: Log in to iCloud.com using the same Apple ID.
The biggest culprits are likely to be Photos, so start with that, and make sure the 'Optimize iPhone Storage' option is enabled. Because you cannot add storage to your phone. It will always have the amount it came with. You have bought space in Apple's synching service, iCloud.
Photos are stored there for 30 days and then deleted from your devices and iCloud. iCloud is not permanent storage nor is it true off device storage. iCloud is really a syncing service, not archival storage.
It will also turn off iCloud, iMessage, FaceTime, Game Center, and other services. Your content won't be deleted from iCloud when you erase your device.
Your original photos and videos are stored in iCloud and space-saving versions are kept on your device. Your library is optimized only when you need space, starting with the photos and videos you access least. You can download the original photos and videos over Wi-Fi or cellular when you need them.
If you no longer want to store your photos and videos in iCloud so that they sync across your devices, you can turn off iCloud Photos for one device, or for all of your devices. To keep your photos safe, download them to your device or save a copy first.
When you charge iPhone it will automatically be backed up to iCloud Over your wifi. A simple and sure test is to log on to iCloud.com (via a browser) using the account that is suppose to have the photos. You can select the Photos icon once logged in, and easily view which photos are already in iCloud.
Your device may still have a local copy of the photos: If you have iCloud Photos turned on and "Optimize iPhone Storage" selected in your settings, your iPhone may still have a local copy of the photos even after they have been deleted from iCloud.
You can delete files you no longer want to store in iCloud Drive. Important: When you delete a file from iCloud Drive on iCloud.com, it's also deleted from all your devices that have iCloud Drive turned on.
On iCloud.com, you can recover files deleted from both iCloud Drive and other apps within the last 30 days, whether you deleted them on iCloud.com or another device that has iCloud Drive turned on. However, you can't recover or restore files you permanently remove.
Erase device: Permanently deletes all data on your device, but may not delete SD cards. After you erase, Find My Device won't work on the device.
iCloud is the service from Apple that securely stores your photos, files, notes, passwords, and other data in the cloud and keeps it up to date across all your devices, automatically. iCloud also makes it easy to share photos, files, notes, and more with friends and family.
If you remove copies of photos and videos on your phone, they're now deleted but, you still can: See your photos and videos, including the ones you just removed, in the Google Photos app and photos.google.com. Edit, share, delete, and manage anything in your Google Photos library.
After reading the overview part, you will know that iCloud Backup backs up almost everything on your iPhone, iPad, or iPod touch, including photos and videos. Whereas iCloud Photos is limited to backup photos and videos rather than apps, messages, etc. So, iCloud Backup can backup more data than iCloud Photos.
iCloud Links automatically expire after 30 days, but you can stop sharing them sooner. In Photos on iCloud.com, click iCloud Links in the sidebar. Click the photo collection you want to stop sharing.
iCloud uses strong security methods, employs strict policies to protect your information, and leads the industry in using privacy-preserving security technologies like end-to-end encryption for your data.
Device storage is the available storage on your iPhone, iPad, Mac, or other Apple device. iCloud storage keeps your photos, files, notes, and more, up-to-date and available across all your devices.