Phones are taking over e-reading

I just saw a Kindle Unlimited ad which shows a woman reading a Kindle book... on a phone instead of an Amazon Kindle! The end of days must be nigh. Funny how after all these years, ebooks are moving to phones in a big manner. I don't believe it's because of the new big phones (though that's it in my case), I don't think enough people have them. So I wonder what happened and why it took so long. (Even WorldReader.org is concentrating on phones these days.)

I didn't see it coming, because to my taste, a screen less than five inches is just not satisfactory for e-reading. But clearly I'm in the minority. It's just interesting to me that it took most of a decade for the general public to catch on.