iTunes automatically backs up your iPhone just in case something happens and it needs to be restored. If you’re not worried about this, there are two different ways to go about stopping it. (This is if you’re on a Mac, if you’re on a PC, just let me know and I can give you those instructions, too) If you simply don’t want this to happen every time, go ahead and click the little x on the right side of the window that displays your backup progress. If you’re looking to prevent it EVER happening when you sync, here’s how you do it:
First, unplug your iPhone and close iTunes.
Open up Terminal.app (Applications/Utilities/Terminal)
After it has opened and loaded, type or copy/paste this text in:
defaults write com.apple.iTunes AutomaticDeviceBackupsDisabled -bool true
Exit Terminal (using the command “exit”) and close the app. Plug in your iPhone and it should skip the backup entirely and just sync the phone with your computer.
If you ever want to undo this, just repeat the first steps (unplug, close iTunes, open Terminal) and type or copy/paste
defaults write com.apple.iTunes AutomaticDeviceBackupsDisabled -bool false
Hit enter, exit out of Terminal, fire up your iPhone and backups should start again!