It IS true.
The only reason it doesn’t seem that way is because for “gamers” (like the people who visit this forum), not much has changed.
But think about all the young kids and older people who back in the day would rock a gameboy just so they could play Tetris. Even several years ago GBAs or DSes were much more prevalent than they are now. For all of THOSE people (and there are a lot more of them than so-called ‘gamers’), phones have already won.
I teach kids 6-15 years of age here in HK and I have never seen one of them ever pull out a handheld console. Puzzle & Dragon and Candy Crush are much more appealing to them.
Why buy a $170-$300 dollar Vita or 3DS console when you can just use your smartphone, which you’re already using for everything else and can easily cover your more basic gaming needs?