iPhone iCloud Backup: How do I include photos on my phone without creating a thumbnail which would delete it off my phone?

I am trying to backup my whole phone, but in the past when I backed up my photos it would delete the actual picture off my phone or leaving a thumbnail. I thought I fixed it by adjusting the settings to stop creating this thumbnail or deleting the photos. Now I am not sure if the actual iCloud Backup is backing up these newer photos. How do I keep all my photos on the phone without removing them from my phone? I don't want to "optimize my phone's space." I have plenty of storage on the phone, but I just want to have access to the photos when I don't have access to wifi or cellular data just to back them up.

I wish apple would just create a way to backup to a external or network drive like they do with time-capsule, so I know my phone is truly backed up.