Idea of Callback Icon
The icon is a logo for the Callback Feature. The icon is what appears to be the shape of an old phone. The phone is at an angle with the top of it to the top left. There is a curved arrow that starts at the mouthpiece and points to the top.
This page contains the Callback vector icon, as well as variations of this icon in different visual styles, and related icons. All icons are in the flat vector style, however, differ by the line thickness, fill, and corner radius.