(Image source from: Body reacts while talking on phone)
We have a habit of moving the body while talking on the phone. Is this a disease or any kind of serious issue..! don't estimate in this way and start fearing for it. Lets get into the details of why this kind of movement will generally be there.
Firstly, keeping the phones that show the video too aside, there will be no visual feedback through the phones. Because of this reason, the body paces and it starts reacting by moving here and there. Even at the odd times, few people have this habit of moving at least in the house. Few people even get accustomed to this habit in such a way that when there is no chance of moving, they drop the phone and avoid speaking through it.
While speaking on the phone, though it is clearly known that the opposite person cannot see us, we usually have a habit of doing some hand movements like warn signs and all. All these are generally because of the absence of visual feedback which turns to a movement in the body and expresses reaction.