Here are Apple's instructions on how to turn off iCloud Photos on one device – or everywhere.
How to turn off iCloud Photos - Apple Support
Note that while you are using iCloud Photos, iCloud backups do not include photos. If you forgot your passcode, and had to reset and erase your phone to get back in, you could restore your photos by turning iCloud Photos on again – you wouldn't need a separate, duplicate copy in an iCloud backup.
Once you turn off iCloud Photos, iCloud backups may start including photos. If they do, you won't be saving any iCloud storage space. Your phone will still try to store all of your photos in iCloud – just in a different "bin" (that is also less convenient to access).
It is possible to manually copy photos from your iPhone to a Mac or PC.
Transfer photos and videos from your iPhone or iPad to your Mac or PC - Apple Support
So if you weren't safeguarding your photos with iCloud in either way (iCloud Photos or iCloud backup), you could still import new photos to a computer from time to time, and back up that computer. But this would require more discipline to remember to do the imports/backups.