You still don't know whether or not the phone is actually listening. This is even worse on cell phones because you can't easily insert something like WireShark

You still don't know whether or not the phone is actually listening. This is even worse on cell phones because you can't easily insert something like WireShark between your cell phone and the data network. Untrusted microphones connected to networks are untrusted microphones connected to networks. The only thing distinguishing an Echo from any smart phone is that you can monitor the Echo's network traffic.