Even if you see it, the hardware could be lying to you! Unless the whole pipeline has support, you get subtly wrong results.
My Firefox on Android happily displays a difference, the webkit logo is very visible. And my AMOLED screen can actually go beyond DCI-P3.
But the phone is cheating. It's "enhancing" sRGB colors to wide gamut by cranking up the saturation accross the whole screen, and the settings are "sRGB" or "DCI-P3", but that doesn't turn off the post-processing filter it just adjusts the strength.
The P3 flowers on that test page in particular look completely wrong on my phone.
There's a visible difference in most of the samples here https://webkit.org/blog-files/color-gamut/