Connect your phone using the USB cable to your computer and let ITunes launch make sure the Summary Page is visible if not click on the Summary button at the top of the iTunes window.
Scroll down to the Options Panel.
De select the Sync this iPhone over Wi-FI option.
In the bottom right hand corner the Sync button disappears and is replaced with two differing radio buttons,one is Apply and the other Revert.
Click Apply and over WI-FI Syncing is off. - This step is the important bit as simply removing the tick is not sufficient.