Figure 1 below shows the measured Color Gamuts for the Apple iPhone X along with the Standard sRGB / Rec.709 and DCI-P3 Color Gamuts. The outermost white curve is the limits of human color vision - the horseshoe is the pure spectral colors and the diagonal is the Line of Purples. A given display can only reproduce the colors that lie inside of the triangle formed by its primary colors.

Accurate White Points
The dots in the center are the measured color of White for each of the Color Gamuts along with the D65 Standard White, which is marked as a white circle. To deliver accurate image colors the display must match both the Standard Color Gamut and the Standard Color of White.

Accurate Color Gamuts
The iPhone X Wide Color Gamut is an accurate match to the DCI-P3 Standard Color Gamut that is used to produce the new 4K UHD TV content. The smaller Color Gamut is an accurate match to the sRGB / Rec.709 Standard Color Gamut that is used for most existing consumer content.

Both of the iPhone X Color Gamuts are a close match to the Standard Gamuts.
See this Figure for the Absolute Color Accuracy measurements for each of the Color Gamuts.