If you have a ton of photos, go through all your photos and delete the ones you dont want, many keep junk photos around and you can delete alot that you dont want. Then go into your recycle bin and delete from there.
If you have a ton of videos then thats definitely a space problems as videos can be LARGE. Any pictures or videos you want to save should be copied to your computer, then deleted off your phone. Then check your space, if it still shows that the space didnt get freed, then turn the iphone off and back on.