Clash of clans not transferring to new device, please help!

My son had an iPhone 4 which he was playing clash of clans on and had another village started on my iPad, both were under the same GameCenter account. We purchased him an iPhone 6 and when we synced the new device the village that transferred was the one on the iPad. He wants the one from his old phone but I cannot figure out how to transfer it and am afraid I will accidentally delete it. Can someone please help me out!?