According to the link another commentor replied to my comment with, which includes the actual per-component cost breakdown, the most expensive part is the Samsung display. Where is that manufactured? Well, in 2017 Samsung was planning the world’s largest plant in... you guessed it... China.
Even if some details or price estimates are wrong, the fact that they are dependent upon a third party for the most expensive component with no obvious alternative is a problem.
Even if Samsung plans to put a plant in China, they still have production capacity in Korea. In fact, most of the components that’s come out of China are fungible like that.
Apple tends to have multiple display providers, even for the same phone model (Sharp, LG, Samsung). They are on top of that problem, mostly.
You provide a very specific definition of "quality" (contrast, brightness, power consumption, color levels, etc, etc) and tell your suppliers to meet it.
Even if some details or price estimates are wrong, the fact that they are dependent upon a third party for the most expensive component with no obvious alternative is a problem.