Something keeps eating up my storage on my iPhone 6+

What is eating up all of my storage space on my iPhone 6 plus even after deleting photos, messages, music and apps? I keep getting the window telling me I'm low or out of storage space. For example, I just deleted the Smurfs off of my phone (600+ mb) to free up space and in the blink of an eye, that extra space was gone and I was back down to zero again. I just don't get it. Any help would be greatly appreciated. Thanks!