Sony MEX-GS810BH - Does the mic connected to the MEX-GS810BH need to be disconnected to use this unit with Amazon Echo Auto as a speakerphone?

I connect my Amazon Echo Auto (Version 1 and now the new Version 2) to my Sony MEX-GS810BH via Bluetooth and set the MEX to Bluetooth Audio to play music. It worked perfectly; I can give vocal commands to the Echo Auto and it works just fine. When I would make/receive a call, I would just press "answer" and the call's audio (including my speaking) comes through the MEX, but people said it sounded like I was in a tunnel. The MEX's mic was connected to it when the unit was initially installed because the Echo Auto didn't exist at that time.

I assumed that I do not need that mic now because the Echo Auto acts as the mic so I cut the mic's cord and removed it but did not unplug it from the MEX's rear because I could not reach it. When I receive/make calls now, the other person cannot hear me at all and hangs up. I could not access the mic's connection on the rear of the MEX, so I just cut its wire and removed the mic.

Does the mic (as connected to the rear of the MEX) need to be completely unplugged from the MEX to now use the Echo Auto as the mic? Or do I need to put the MEX on a different setting instead of Bluetooth Audio to make and receive calls? I don't see anything in the MEX's user manual about "disabling" its connected mic.

I hope someone here can answer this issue! This MEX is out of warranty now, so Sony Customer Service and Tech Support will not assist.