Do you mean technically? On a speakerphone with hd quality... Possibly. There's lots of research about audio side-channels.
In practice though - why would they do that given Echo is designed to work with network connection?
Just comming from a luddite , maybe there is a bit of buffer space incuded in these devices that could be shared with the cloud masters to tally my outbursts when responding to the capitalistic fascist media playing in the foreground of my thoughts?,!? Just sayn...
Oh and to answer you're question, what if network logs actually mattred?