icloud drive uses too much space on my iphone, over 80 gb

Nakatami wrote: … It should keeps my data in cloud, not on my device.

What it should do depends on the situation. Can you give us more information?

• At Settings>General>iPhone Storage, what does it say? For instance, mine says 47 GB of 128 GB used. How about yours?
• At Settings>Apple ID>iCloud what does it say about your Storage?
• Do you have Optimize turned on Photos?

Have you tried a forced restart? 

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. 

You may have misunderstood the purpose of iCloud. It is a syncing service to make the same data available across devices, it is not an external storage solution. Using Optimized Storage can ease device constraints on storage by offloading files that are not used frequently, but in no way is it an extension of device storage.

To manually remove files from your device, where they will remain in iCloud.

• Open the files app and choose the Browse tab
• Select the 3 dots on top of the screent
• Select View Options, then choose size to sort the files by size
• On the ones that are being stored on your iPhone, tap and hold and choose "Remove Download". You will then see the iCloud symbol next to the file where the local copy has been removed and it will be downloaded again when needed.

As for the large amounts of data being stored on your device, I would review the apps that have permission to access your files on the iCloud Drive. Any of these apps can initiate a download of those files.

• Go to Settings > [name on top] > iCloud > iCloud Drive > Apps Syncing to iCloud Drive
• Start with 3rd party apps and switch them off to test.
• After manually removing the files from your device where they remain in iCloud and switching off third party apps that allow access, verify your problem is solved by the files not being downloaded to your device again, then turn each third party app on one at a time to identify where the issue is coming from.

And finally, if you have not done a Force Restart previously, I would recommend to do that now. This will clear any corrupted cache files and something I do after every update just for basic house cleaning. It may take a couple of attempts to get the speed and sequence of the key presses correct.

• Press and release quickly Volume Up.
• Press and release quickly Volume Down.
• Press and HOLD the side button until the Apple Logo appears. This could take up to 15 seconds while holding the side button until you see the Apple Logo and you will want to ignore anything else on the screen during that time.

Wow! 249 out of 256 GB used? Wow, again! You should be keeping at least 25 GB free-- Apple recommends keeping at least 10% of the storage free. Lots of stuff just can't get done without the room to turn around. The iPhone may not even be able to delete pictures or files with so little space available!

You may be able to free up some space by dumping applications. You get two choices in that-- you can delete only the app, which may not use much memory, anyway, or you can trash the app and data which may relieve a good bit of congestion.