I'm no expert - but I understood the whole reason Foxconn et al. exist in their current state is because the labour in China is so cheap I that it makes financial sense to manufacture there. But if the bulk of the labour expense is taken out of the equation what's the benefit of having the manufacturing in China anyway? Why not build the automated factories in the US?
I'm asking seriously as I don't know.
There are a lot of reasons.
Chinese infrastructure is vastly superior to the US'... I'm talking ports, railway, etc. They've invested heavily in this. No other country compares really.
Materials are cheaper there, due in part to the lack of environmental regulations (those that exist are rarely enforced). Many of apples products use aluminum, which China produces more than 50% of the worlds supply. Factor in rare earth metals, which China pretty much has a monopoly on... you see where I'm going with this.
Almost all electronic parts are made there, or in that general area, which saves a ton on shipping. Manufacturing an iPhone in the US would require that all those parts be made in the US, or ship them from abroad ($$$).
In addition to low wages, Chinese workers have no rights and few benefits, which not only makes running factories cheaper, it makes their factories highly customizable (ie you can lay off workers at need, etc). Unions are illegal. They aren't entitled to vacations, sick leave, etc. There's no employment insurance to pay or disability benefits to pay, etc. Coupled with this is an ample supply of both skilled and unskilled workers.
The government is very pro manufacturing. Meaning that (usually with a small bribe of course) you can build a shop with very minimal pushback. Coupled with the lack of environmental regulation (think of waste dumping)... makes for a lot of convenience... and savings.
There are more I'm probably not thinking about..
Essentially, unless Americans want to sacrifice their environmental laws, invest trillions in infrastructure and force everyone to make electronic components in the USA (which would take a long time), it's not going to happen. It's definitely not going to happen while paying its workers a living wage.