ICON??? Blue and black rectangle with diagonal "+" dividing

So I have never seen or maybe just never noticed this icon before. It shows on the screen when I am making a call( phone is ringing on the other end) and while I am talking to the person on the other end. It is in the top right corner of the screen. Its a rectangle with a line of 5 "+" signs going from the top left to the bottem right, of the......