Create a virtual Mic and route real mic to it

Hello. Id like to process my microfone input to remove the voice eco from SoundBox.

im using a softphone on windows that my output voice goes out to a soundbox located on a totem with a mic. and this softphone receives the custommer audio trought it to.

Im having a problem that when the atenddence speaks the spoken audio returns from SoundBox to microfone and make the custommer hard to listem.

Im using REAPER and ELEMENT and i installed Virtual Audio Cable on my windows but i dont know how to make it work. 

please some one can help me? Its for a personal project but i can pay for consulting to solve it.