I need to use the phone a lot on my bike and I have the same set-up as you do. The problem is that when you speak it operates a 50% mute on incoming volume,
Cheap and easy but hard work solution is use what I call radio discipline, i.e you speak. STOP then they speak. STOP etc. It works but it's not ideal.
I resorted to going into Autocom as they are only 1/2 hour away from home.
For £20 they removed the vox operation 50% mute and now it's perfect.
I honestly think they should be set-up this way out of the box.
Unsure if GS Rich will be able to tell you how to do this if it is DIY-able, but it is a worthwhile mod and well worth the effort. I've had this done on both my bikes now
Hope this helps
Roger.