Corning is listed as having locations in Kentucky, Taiwan and South Korea [1]. Why would they be making mass manufactured components in Kentucky if they have plants in Taiwan and SK? Most likely Kentucky is only responsible for initial engineering samples and/or creating equipment for mass manufacturing.
From your link, this is what’s said:
> While the iPhone is mostly designed by the Apple team in the US, its components are provided by many countries around the world.
This is claimed to be supported by [2] so let’s follow that chain. Here’s all the link says:
> Still, reports are coming in that US companies involved in the Apple supply chain are beefing up their US production facilities and many of the components that go into the iPhone are actually made Stateside and shipped to China for assembly.
No attribution. No evidence. Just an unsubstantiated claim.
Your source also says this:
> Several companies around the world also contributes to the making of iPhone. For example, the French-Italian company STMicroelectronics manufactures iPhone’s gyroscope that allows people to change the display from vertical to horizontal. The Dutch company NXP Semiconductors provides the M7 Motion Coprocessor that can gather the motion data and use it to measure health and fitness.
But again. Those devices are getting designed in those countries but they get mass manufactured inside Asia. The evidence for that hypothesis is that Apple’s supplier list contains manufacturing locations in Asia for those suppliers. Maybe they do local manufacturing for development samples they deliver to Apple or they manufacture various supporting machines for the assembly line (eg calibration machines for audio and sensors) but the components themselves almost certainly are made in Asia.
This page is a bit out of date, but I don’t think that the sourcing of parts has changed all that much. https://u.osu.edu/iphone/fsdfsdff/