Will iTunes sync new phones, can't restore old phone's backup?

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iTunes syncs new phone, can't restore old phone's backup

I am trying to restore the backup of my old phone to a new phone. I backup the old phone fine using iTunes, but when I attach the new phone, iTunes syncs it, and the old phone's backup is gone.

How can I get the new phone to stop syncing so I can restore the old phone's backup?
(unchecking "Automatically sync when this phone is connected" doesn't work.)