iPhone 5c photos not downloading on iCloud

Hi,

This is my sons iPhone 5c phone.

I am trying to free up space for him and is showing phone storage is all used... none available. We are unable to download any apps or take any photos. Storage full.

But I have paid for iCloud storage and it is showing he still has 43.37 GB available.

Could someone help me on how to manage the storage?

Many thanks