Half my Storage on iPhone 5c is not even stuff on my phone? How can I get more storage?

So all the apps and stuff on my phone only add up to like 2.5 GB and I have only 5 GB on my phone. The other 2.5 GB is stuff I don't even know exist. I want it gone because I'm tired of having to delete everything and now I can't even open up some apps because of it. How can I get rid of this invisible storage? (Whenever I delete stuff the empty space is usually filled up again by stuff I don't even know).

The invisible storage is memory used to make your phone run correctly. This is why I'm not a fan of Apple Iphones. They say that they have 8GB of storage, which is true. But they don't tell you that half of that storage is used by the phone to make it work.