So you bought that new iPhone. If you are like the typical owner, you’ll be pulling your phone out and using it some 80 times a day, according to data Apple collects. That means you’ll be consulting the glossy little rectangle nearly 30,000 times over the coming year. Your new phone, like your old one, will become your constant companion and trusty factotum—your teacher, secretary, confessor, guru. The two of you will be inseparable.

The smartphone is unique in the annals of personal technology. We keep the gadget within...