What is the point of iCloud?

Hi MeganMayday,

Thanks for contacting Apple Support Communities!

We understand that you're concerned about your iPhone storage being full while you still have space available in iCloud.

iCloud keeps your information up to date across your devices so you can access the same information from other devices. It doesn't increase your iPhone storage. You can enable Optimize Storage for photos stored in iCloud which will keep smaller space saving versions of your photos and videos on your iPhone while the full resolution photos and videos are stored in iCloud. You can learn more about iCloud Photos here: Set up and use iCloud Photos - Apple Support

"If you need to save space on your device

iCloud Photos keeps all your photos and videos in their original, high-resolution version. To save storage space on your device, you can turn on Optimize Storage.

If you turn on Optimize Storage, iCloud Photos automatically manages the size of your library on your device. Your original photos and videos are stored in iCloud and space-saving versions are kept on your device. Your library is optimized only when you need space, starting with the photos and videos you access least. You can download the original photos and videos over Wi-Fi or cellular when you need them."

This is also a great resource which will show you the difference between iCloud and iPhone storage: What's the difference between device storage and iCloud storage? - Apple Support

If you need help to manage your iPhone storage, this is a great resource for you: How to check the storage on your iPhone and iPad - Apple Support

We hope this helps.

Cheers!