0 bytes available even though the apps on my phone aren't close to filling the 16GB. I don't sync with iTunes, all I do is debug apps with Xcode. On iTunes it shows that "other" mostly fills it up. It's iPhone 6 Plus OS 9.2.1.
I have already hit "Erase all content and settings" 3 times, it works until I connect it to my computer and debug an app I'm working on on Xcode - (I delete the app after I use it too).