Search around for information regarding Other storage. It was common in older WP8 releases, but I believe it was fixed with either GDR2? or Update 3 (aka GDR3)
These are those files which are needed and are the files which u even downloaded which r not images of phones or any other format which ur phone can specify
Also these included some system setting files which are taking up the space.. So dont worry u cant remove these files
But yes u can by formatting ur phone and installing all d apps again. Then u will find that ur phone's free space is increased...