Brownian Phone Motion

Why do people invariably want to walk around when talking on their mobiles? When you receive a call do you feel an irresistible urge to wander? I noticed this a few days ago when I was trying to take a photo of a building. A guy on a phone popped into view, saw that he was blocking my shot and disappeared again. But then not long after, his random phone motion again brought him into view. Clearly he had no control of his legs. Somehow the navigation circuits in his brain had been disrupted by his talking and he was not fully aware of his location. 

I've noticed this myself, taking a call and then being fully absorbed in a chat and suddenly finding myself in the  garden shed with no memory of walking there. Can some neuropsychologist please investigate this issue? There's definitely a Nobel prize in this.