Other Storage On iPhone
Other Storage on iPhone consumes a large chunk of the available space on your iPhone. In this guide, i will explain the steps you can take to fix this but before you proceed, make sure that you back up your iPhone on iTunes and iCloud incase something goes wrong; you should be able to restore it.

Step 1:
Assuming that your iPhone is connected to iTunes and has synced (if not then do it) and you are seeing other storage consuming space. Uncheck sync music in iTunes.
Step 2:
Install the iPhone DiskAid trial software on your computer. What this software does is that it opens your iPhone’s disk in an explorer view allowing you to transfer files. Locate and Open Media Folders from here.
Step 3:
Go to iTunes control folder and open the sub folder Music Folder. In this sub folder, you will see a number of sub folders starting with f.
Step 4:
Delete and remove all subfolders in Music because this is where the files hogging up your Other storage resides.
Step 5:
Now open iTunes and while the music sync is still turned off, sync your iPhone so it can remove all music files, and keep the other content. We will resync music later.
Step 6:
Once it has finished syncing, unplug and reboot the iPhone by holding the home button and the sleep/wake button together until you see the white apple logo.
Step 7:
Now connect the iPhone back and put a check on the sync music option and re-sync the iPhone. This will sync the music back to your phone.
If your iPhone is jailbroken then delete the samesub folders in the PWNTunes Control Folder.