Hello Cxssi,
Thanks for posting in the Apple Support Communities. We're happy to look into this with you. First thing we'd suggest is to make sure that iCloud Photos is enabled in your settings, and enable Optimize iPhone Storage, if it's not already.
- Go to Settings
- Tap your name
- Select iCloud
- Tap on Photos and review to see if Optimize iPhone Storage has a checkmark to show its enabled.
Manage your photo and video storage - Apple Support
As for Messages in iCloud, this is more a syncing service, to ensure that your messages appear the same across all your devices. The only option for reducing the amount of storage used by messages would be to delete messages you no longer want or need. You could also change the setting for how long messages are kept before being deleted by going to Settings > Messages > Keep Messages.
Use Messages in iCloud - Apple Support
We hope this information is helpful. Let us know if you have additional questions.
Best regards.