Can you give us more information?
- Are you using iCloud Photos to synchronize your devices?
- …Do you have “Optimize Storage” checked in Photos’ Settings
- ...Do you see all your iPhone pictures at iCloud.com?
- ...Do you see all your Mac pictures at iCloud.com?
- …Do you have more than 10% free storage on your iCloud account?
- …What does your Photos say in you account icon, ike this?
- Do you have more than 10% free storage on your iPhone?
- Have you tried a Forced re-start?
Force restart iPhone - Apple Support
This is different from a simple Power Off. I had to continue holding the button down past the "slide to power off" message, and then I released the button only after the Apple Logo appeared indicating a re-start.
Be very careful of 3rd Party apps claiming to i"mprove" Photos -- we've seen bad, bad results.