Hi there, Shyloh2012.
It appears that the game Big Fish Casino on your iPhone is using 6GB of storage, and we're glad to provide assistance.
Restart your iPhone - Apple Support -- See if restarting your iPhone removes the excess data it seems to be using.
How to back up your iPhone, iPad, and iPod touch - Apple Support -- Before proceeding, please create a fresh backup of your iPhone.
How to delete apps on your iPhone, iPad, and iPod touch - Apple Support -- If you're still seeing a lot of data being used by the app, delete it and restart your iPhone again. Once your iPhone is back to the Home screen: Redownload apps, music, movies, TV shows, and books - Apple Support and check the storage once again.
Get back to us with the results including which model of iPhone you're using and the iOS it's currently on.
All the best.