Earlier quoted context omitted.
My theory is that economies of scale for 5.5 inch 1080p touchscreens in mainland Chinese manufacturing make it a lot cheaper now. That is just about the most common screen size and not the higher than 1080 resolution found on high end phones.
The LCDs are probably not made in mainland China though, and ASUS is still Taiwanese.
http://www.boe.com/en/index/pei.html
http://www.tcldisplay.com/en/home/index.html
http://www.visionox.com/en/index.aspx
http://www.everdisplay.com/en/
The LCD and OLED panel in your phone is more likely made in China by a Chinese company, the irony is now that even Samsung had use Visionox AMOLED in their phones especially recently because they were constrained with supplying their OLEDs to Apple.
ASUS does not make displays the only Taiwanese display manufacturer is AU Optronics IIRC and they don't make small and medium size displays.
The only thing that China still doesn't do well are large screen OLEDs (LG is now building a factory in China for that) and that's about it. China is oddly pushing AMOLED to the limit and are leading the development as far as flexible displays go much further than Samsung or LG do at least publicly.