The only way to turn it off is to go into Windows Services and turn off the service.
There’s just one problem. I use an iPhone. I can't disable it. But doing so for a little while dropped the CPU meters to nothing. So I now have more motivation to migrate to a new phone beyond just having one with a larger screen. This problem has been known for years. AppleMobileDeviceService.exe has been in iTunes since version 7.3. People complained on the Apple boards more than two years ago that it was consuming up to 50% of CPU cycles, and thus far it's as bad as it always has been. Mind you, Mac users aren't complaining. Just Windows users.