Systems taking up 120gb of dad’s phone!

Hey all,

My dad’s iPhone 6 has been acting up (slow to respond, ***** itself down, hangs for a while, unresponsive, etc). After checking Settings > Storage, I found that his Systems is taking up 121 GB of space. He really doesn’t wnt to loose som of his data but no mbackups, wethere iCloud or iTunes, have worked. Any advice? Most of what he needs is in WhatsApp, but it says it needs 25 GB of storage to do so, and we can’t figure out what’s going on.

Thanks