Funny how Nicholas Carr's "How Smartphones Hijack Our Minds" in the October 6, 2017 1 issue of the Wall Street Journal echoes Socrates who believed that writing would also weaken our intellect. Let me offer an alternative. Off-loading some functions to our pocket computers frees the mind to pursue other things. I have posted about the notion of the Human/Computer Centaur before. Chess masters have discovered that human/computer teams win more games than either humans or computers by themselves. Here is a link to a PARC blog "Half-Human, Half-Computer? Meet the Modern Centaur"about modern centaur hybrids.
Just as Socrates couldn't foresee the benefits that would accrue from a culture that could write things down, share thoughts across generations, etc, I don't think Carr can see where we're going, for better and for worse. He is looking through a rear-view mirror. http://blogs.parc.com/2017/01/half-human-half-computer-meet-the-modern-centaur/
Classic Greeks lost a vast capacity to memorize when they adopted writing, but they gained the capacity to analyze, to separate themselves from and critique the material of their culture and they gained the ability to speak to generations beyond an individual's death. The memory exercises we all were given in grade school are merely the cultural residue of a previous human state of existence where memorization was the ONLY way to preserve a culture's heritage. We think they made us smarter for the same reason we extravagantly reward our modern bards for singing love songs to us. Cultural residues are from a time when memorization and singing were paramount. There are always winners and losers when there's a technological paradigm shift.
I'm not saying we'll be better off in the "computer with a cellphone app future", but we can't really see right now, except through a rear-view mirror, whether we'll be worse off. Bottom line, it's going to happen and what we need right now are defenses against the trolls, bots and fake-news-propagating social media that exploit the weaknesses of a transitional population.