Storage

Tap Settings > [your name] > iCloud > Photos. Tap Sync this iPhone. In iOS 15 or earlier, tap to turn on iCloud Photos. Select Optimize iPhone Storage to save space on your device.

Manage your photo and video storage - Apple Support (IN)

Enabling iCloud for Photos, Notes, Videos, Reminders, Messages, and more, as depicted in the provided picture, means that if you delete any or all data from one device, it will also be removed from iCloud and all other devices linked to the same Apple ID. Likewise, the reverse is true as well.

Alternatively, you may have to upload it to iCloud Drive

1. Settings > [Apple ID] > iCloud > iCloud Drive [Enable]
2. Download the Files App from the App Store
3. Now, select photos and tap on the Share icon (Bottom LH side)
4. Then scroll down and tap on Save to Files
5. Choose a folder or create a new one.
6. Tap Save (Top RH side)

Now you can safely delete it from the iPhone.