His question was not asking about energy efficiency, but rather what is the holistic point of it all. And he is correct that the energy efficiency is scam. The real goal is enslavement of the developing world by loaning a smartphone in exchange for unnoticed electricity usage.
His question was exactly efficiency. I answered both with respect to energy efficiency (much better than the best ASICs as currently deployed, given effectively free electricity) and overall efficiency (likely also, since the chips will likely be very cheap). If I recall correctly I also said I didn't think it was a particularly good idea, regardless of efficiency.
He didn't ask about Larry Summers, etc. That's fair game for you be interested in talking about, but not what he asked.
Is it possible for a toaster/phone + mining chip to be as/more efficient than the best ASIC's on the market, and if it is not, how can this be a cost-efficient way to mine?
Cropping what he wrote doesn't help you. It is clear to me he was asking what the overall economic point is, and he introduced energy efficiency as one of the aspects that doesn't give him a holistic understanding. If you then argue that efficiency is improved in irrelevant and insignificant markets, you create holistic myopia instead of understanding.
Larry Summers participation is irrelevant to whether there is a usage case for the excess heat which makes a significant economic argument. I can't think of one.