Last fall, Andrew Vestal found himself rocking his baby daughter, Ada, back to sleep every morning between 3 a.m. and 5 a.m. Cradling Ada in the crook of his arm, he discovered he could read his dimly-lit phone with one hand. That’s how he read David Mitchell’s 624-page science-fiction saga “The Bone Clocks.”

Mr. Vestal’s iPhone has offered him a way to squeeze in time for reading that he otherwise might have given up. He reads on lunch breaks. He even reads between meetings as he walks across Microsoft’s Seattle campus, where...