Can I delete photos off of my device without deleting them from my iCloud backup?

If you mean from iCloud Photo Library, be aware that is not a backup. iCloud Photo Library is a syncing service. Any photo you delete from a device where iCloud Photo Library is turned on will also be deleted from iCloud and from any other device connected to that iCloud Photo Library. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See: iCloud Photo Library - Apple Support

Apple does not currently offer cloud-only storage for photos. If that is what you want or need, you may want to explore 3rd party options such as Google Photos or Dropbox.

Another way that photos may be on iCloud (if you don’t have iCloud Photo Library turned on) is via a backup of an iOS device. The only thing you can do with a backup is use it to restore a device or set up a new device. The contents of backups are not viewable at iCloud.com and if you delete a photo from a device it will not be included in future backups and will be lost.

Deleting photos does not delete them form yoru IOS backup

If you are using iCloud Photo Library it is not a backup service nor is it an offsite storage service - it is a syncin servic and andy change (addition, deletion or edit) made on any connected device is made on all connected devices

this mayhelp you under the many different iCloud services available - iCloud Deconstructed

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