Why does my phone say i'm using 11.75 of GB when i'm not?

I have a iphone 6 and in storage settings it says i'm using 11.75 GB of space. I deleted all the apps that i had before and the only app i have currently that s using the most space is photos which is using 179.1 MB of space and the rest of the apps which is messages, mail, health, calendar & reminders, safari, voicemails, and sounds are all using less than 100 MG. Of space which is only 8 apps that already come with the iphone. I don't know how to fix this problem.

The operating system takes up space as well. Delete your browsing history, or download an app that cleans your phone out, deleting old unneeded data. Also check your photos, upload them to a cloud somewhere and delete them off your phone. ICloud is a great place to store files.