Knowledge is Power

Not really, it's cause when you would normally talk to someone our brain is recognising all the other emotional signs of a person like facial expression, posture, tone etc that we are talking to. When you're on the phone you lack that, however, your brain still wants to respond to that person physically. Hence why you tend to move your arms or walk while on the phone, the brain still needs to translate your emotional responses into physical gestures.

[Citation needed]