I accidentally drove up to the Tesla factory in Fremont during afternoon rush hour. It could have been worse, but I was stuck in a line of cars for like 10 minutes just trying to get back out from the road that leads in (and there are two exits).
Foxconn is 10 times that. Obviously they "solve" the problem with a dorm, lock-ins, and other abuses. We wouldn't do that here, but we don't have the same infrastructure.
However, if we wanted to, we could have a plant assembling more iphones with fewer far workers, probably with minimal cost increases to the iphone.