I am currently going through Phoenix Inside Out by @shankardevy, it gets just into enough details to remove the too much abstraction that may be. For example, before reading it I never understood why we have both template and view directories, he goes in and explains how Phoenix creates a function for us (you get to create that function and see that it really works as expected
Second great thing I love about it, it introduces testing with Phoenix - this is awesome especially now that I have first-hand experience as to why writing tests is important
I havent finished going through it yet but I would recomment you have a look at it
He actually has a post about it on elixir forum
