the audio controls use the same height as the chat window and this may be really small. And they are included in the window and not flipped open to make the window larger as long as this is possible.
So it may be a good thing to change the min-size of the window to make sure that the audio controls can be displayed properly. And one could think about using the full height of the window for the audio controls. And of course about flipping them open instead of shrinking the chat and input area of the window.
PS: An option to reject incoming calls for the next n minutes or to disable them for some hours would also be fine, such a ring-ring can be annoying.