https://pragmaticstudio.com/phoenix-liveview
Those are the videos I've been watching just to get a better idea of the concepts -- I agree, they are well made. I actually found them via HN about a week ago.
I'm thinking of reading this once I finish the videos: https://pragprog.com/book/phoenix14/programming-phoenix-1-4
I really like that course because you basically hack a web server together, and then refactor it to be kind-of like the Phoenix architecture, which for me is the perfect way to learn something like that. Toward the end they do the same with GenServers - hack together a stateful server, and then refactor it so it looks like a GenServer, before introducing the actual thing as a drop-in replacement. That's where I've got up to so far, but I'd definitely recommend that course if that sort of thing appeals to you and you like their teaching/video style.
That book looks great too, thanks for sharing :) Reading the author section, I'm definitely tempted to pick up a copy.