Same for Sony, LG, etcetra.
https://www.pcworld.com/article/2023286/foxconn-samsung-face...
But Samsung has facilities in China too:
https://www.samsung.com/semiconductor/about-us/location/manu...
Another 2012 article about labor practices at Samsung factories:
https://www.theatlantic.com/technology/archive/2012/09/these...
The point is everyone uses cheap labor for manufacturing if possible, whether it's China or elsewhere. If they did not, then their mass market products would probably be priced too high and customers would reward competitors and they would go out of business. No one is paying higher paid people in South Korea or Japan to assemble phones if it can be done drastically cheaper elsewhere.
Another article about Sony using Foxconn and other ODMs:
http://www.xperiablog.net/2012/06/19/sony-mobile-partners-wi...
I assume LG and Samsung are big enough to have their own facilities and be ODMs themselves, but I would guess the smaller players like Sony have to outsource to them.
Fact is, they do manufacture phones in South Korea. Not all their phones, but they do manufacture them. Evidently it's still profitable enough to do so, and evidently they do not charge $10K for their top-of-the-line Galaxy S phones made in SK. https://www.businessinsider.com/samsung-gumi-factory-2014-5?...
Sony has also made phones in SK and Japan.
Obviously these are not contenders for the cheapest phone, but we weren't talking about the cheap Xiaomis and Huaweis anyway. And evidently lots and lots of people are happy to pay for more expensive phones. Apple has ridiculous profit margins and people still pay for it.
I assume if Samsung had figured out how to make phones with better labor practices than Apple, then they would be advertising it. Seems like pretty easy PR points to win business, so I would have to wonder why not? I am guessing it is either inconsistent across their product lines or labor practices are increasing over the years.