I watched this yesterday. Great stuff. I downloaded the linked paper by Dr. Phillips. The Terrain-Theory did get taken a bit far in the woo-woo world (I look through a yoga looking glass) during a recent cough pandemic because magical thinkers took it as appositional to germ theory. I can imagine this doctor is regarded as extreme by the mainstream. But the well presented content of the talk is sensible. He just wants to change the medical illness industry, like Dr. Unwin does.
The germ theory is pretty well-established, and it does apply in the case of infectious diseases. I took Dr. Phillips’ point to be that that sort of thinking doesn’t work in the case of the chronic diseases that plague us. I like the idea of viewing them not so much as “diseases” but as bodily responses to an unhealthy stimulus.