Do you ever go to your smartphone for a particular purpose - to check your weather app, say - and, on the way, forget why you went to your phone in the first place? It's like walking into a room to get your reading glasses only to forget why you walked into the room. You pause, look around, and wonder, "What the hell did I come in here for?" You look around and decide you have to leave the room in order to recall your steps and, therefore, hopefully, your thoughts. The motivation for walking into the room in the first place.
Oh, but I do that with my phone. I pick it up for a specific purpose and see notifications that clearly need attention: email, Facebook, past due reminders, Words With Friends. I feel compelled to clear them all and when I do, I can't remember what I picked up the phone up for in the first place.
It certainly wasn't to make a phone call.