If I have read their website right, they say only first three modules are free, the whole course has 35 modules.
> there seems to be a host of free videos on YT as well as many books on elixir/phoenix
You are right about the videos, though I am not so sure about books. Phoenix 1.7 doesn't seem to have any good books for it at all.
You are also right about that the Phoenix book needs an update, they changed A LOT with the way they structure code in the last release. Which, you don't have to use btw, you can still use the older methods. The major differences are here https://elixircasts.io/upgrading-to-phoenix-1.7 which I can honestly understand the pain a new developer feels when the books are out of date.
I'd still consider going through an older book, you'll learn 90-95% of the same thing.
Seconded. I have the book, and it's pretty easy to understand where the differences are. And worth learning the pre 1.7 Phoenix because a lot of the changes thereafter make so much more sense when you know the pain points that motivated them.