On a normal size phone screen it's easy to make out the words for me with normal vision

If 10 was as easy as black on white and 0 was invisible as a solid color, I'd rate this graphic as a 6.5/10 in difficulty. You can clearly read it in less than a second, but you will probably spend the rest of the second and part of the following second looking for the edges of the letters and double checking it says what you thought it said and not something else. They are somewhat dull reds and greens, but they are visible. If you are having too much trouble then perhaps your phone display settings may need adjusting.

For me, it was easy.

Worth noting that there is such thing as color deficiency where specific colors appear more dull than they would for others. It isn't technically colorblindness but could still make it harder to read these tests.

One of my friends has this with red colors but could see everything else normally, and he described it as red looking way more desaturated than other colors (almost like a brown/gray?).

All I see is dots.