Why is my iphone storage filling up with videos after everything has been backed up to icloud?

Ok so basically I shoot a lot of 10 bit 4k video from filmic pro on my 13 pro for youtube. The footage has been adding up and my phone is now 215/256 gb with 186 of those being the photos app. The Photos and videos have all been uploaded to icloud already automatically overnight and manually. But the storage is not freeing up on my phone. I just want to know what I should do to get the local storage to go down without having to delete them off my phone, and in turn, the cloud. Thanks.

Set the Photos app to optimize your library. It will then push off actual content as it requires and replace it with thubmnails.

iCloud Photo Library is not separate storage, it is a sync solution.