Check out how to turn off automatic syncing for your iPhone.
If you want to stop the automatic syncing function of your iPhone as it does with the computer it usually connects with, you can try these steps:
1. Plug iPhone in your computer to connect it.
2. Go to iTunes.
3. Tap on iPhone in the Devices list.
4. Select Summary at the top of iPhone screen.
5. Remove the tick from “Open iTunes when this iPhone is connected”.
Now you can keep syncing whenever you want by selecting the Sync button without syncing by default.