Default use phone as bluetooth headset

I've been able to use Osmart master and Omate companion to send notifications to my watch from my phone, but, my question is, if I have my sim card installed in my watch, is there a way to answer calls that I receive on my watch using my phone as a bluetooth headset? I thought I read somewhere that the apps should work in reverse too, but I can't seem to figure it out. I was going to try and install Omaster on my watch and companion on my phone, but I can't find companion in the google play store, and I don't have the Ostore on my phone. Anyone know how to do this? Thanks!