You can set ‘F’ keys, the function keys along the top of the keyboard, to answer incoming calls, or to ring the number you cave copied onto your clipboard.

Right click on the busylight icon in your task bar

Select “Lync, SfB tools”

I used F3 for Fast Dialout, which uses the number you cave control-c copied onto your keyboard to dial out with, and F4 to answer calls.    If you use Horizon, or another app that uses Function keys, you might want to select the windows key in conjunction with it.