DisplayMate posted a review of the iPhone X OLED display (5.8" 1125x2436 Samsung-made flexible Super AMOLED). Samsung's own OLEDs are considered by DisplayMate to be the best displays in the world, so we expected this display to be excellent - and DisplayMate confirms it is actually better than Samsung's own displays thanks to impressive precision display calibration that Apple developed that transforms the OLED hardware into a superbly accurate and high performance display.
DisplayMate confirms that this OLED is indeed the brightest full-screen OLED smartphone ever. The iPhone X also offers the highest absolute color accuracy ever tested (visually indistinguishable From perfect), the highest full-screen contrast rating in ambient light, the highest contrast ratio ever (infinite as in all OLEDs) and lowest screen reflectance and the smallest brightness variation with viewing angle.