How to stop the iPhone Auto Backup
There isn't a way to turn off the Auto Backup every time. You can choose to turn off auto syncing in the iTunes preferences, which turns of syncing and backup. But you're probably like me and just want to stop the back up that takes 30+ minutes every time and only want to sync.
So the best way to stop the back up is when you plug your iphone into your computer and you see the status bar at the top of itunes say "Backing up iPhone" click the little "x" to the right to stop the process. It will stop the back up and then continue normally with just the syncing.
I hope this helps as it was quite annoying to me as well. Hopefully Apple will come out with some settings within iTunes that allow you to choose when you want to backup, like maybe once every 3, 5, or 7 days or manually.