Quite a few of my students have said great things about Phoenix in Action, from Manning, and it looks to me like a fantastic resource for beginners. Elixir in Action is also top-notch and will show you what's special about the BEAM.
Great book though.
The auth generator is just a new feature. Learning how the pieces work from the book is still worthwhile.
My advice if you want to avoid confusion as you're learning is to just use the same version of Phoenix the book does! (1.4 in this case)
After you go through it, you can follow the official upgrade guides in just a few minutes.
I liked the book Programming Elixir 1.6 By (Pragmatic) Dave Thomas. Solved the exercises. Did not quite find use for macros. And I have not done any production projects.
The pragmatic studio has some courses for the space: elixir, OTP, LiveView, etc. and free tutorials. The quality is good. Simon Thomson's course on futurelearn was also good. https://pragmaticstudio.com/ and https://www.futurelearn.com/
A recurrent problem for me though has been to write an application. I used to write java's petclinic/petstore application when learning a framework, library, etc. Have not been able to do so with some other ecosystems... perhaps laziness, perhaps have not been able to answer why. And languages in isolation have not clicked for me much apart from maybe making me think in different ways.
Why does this Erlang/Elixir/BEAM interest me then? A colleague who talked highly of it... Then there's Joe, his talks, and Alan Kay's recommendation has Joe's thesis on recommended reading list: https://news.ycombinator.com/item?id=20653453
There is also Erlang Masterclass series 1,2,3 starting here: https://www.youtube.com/playlist?list=PLR812eVbehlwEArT3Bv3U...