iPhone 6 storage full

Hi all,

My own iPhone broke in pieces and so I am reviving another obsolete phone that has been in the drawers since my wife switched plans. It only has 16GB memory and I try to purge as much from my backup as possible. Majority of the phone's storage is taken up by 'Photo's' and 'Other'. However, there are no photo's on the phone (nor a folder 'recently deleted' or anything like that, not in the app 'Photo's nor in Settings>General>iPhone Storage>Photo's). Neither can I find anything in iTunes, when hooked up to my pc.

It is my main issue with Apple; I don't know where the files are, let alone have any control over them. Can anyone help me find these 4.8GB worth of photo's and how to permanently delete them?