Precision machining still exists in America, it's just all focused towards aerospace and weapons manufacturing.

Apple would simply have to pay such people a wage competitive with what they receive from aerospace and weapons production. Which would be a lot but not hit the bottom line of an individual iPhone that much given that it's mostly to do with people who have experience setting up automated factories, CAD/CAM programming etc, rather than producing a single unit of whatever.

The article is also dumb given that they're pretending the unit cost of an iPhone is $3000 rather than accurately understanding that the actual cost is vastly less and Apple simply massively overcharges, and could take a hit to their profit margin while onshoring production, or (more likely) offset the cost to their users and it'd be more like $3500 or $4000 rather than $30000 (ridiculous made up number with nothing backing it, obviously).