In that case I would start with Programming Elixir or Elixir in Action - or both! I loved both but if you can only get one simply read the preview chapters and go with whichever author feels like they’re on the same wavelength as you.
Here are my reviews for each:
And
Saša Jurić is also very active on the Elixir Forum so check out some of his posts, and here’s PragDave’s profile - tho unfortunately last I heard he’s no longer using Elixir. You can’t go wrong with either book tbh - just follow your heart and go with whoever’s writing style your prefer.
Some of the other books I’ve read and have really enjoyed are…
And I started Programming Phoenix but have decided to read it last - just before I start working on a Phoenix app because I feel out of everything, the Phoenix stuff will need to be fresh in my mind most. Here are some of my comments tho:
I am also in the process of reading Programming Erlang and and loving it!
Honestly tho, I don’t think you can go wring with any of the books from PragProg or Manning, and (especially with out discount) they are so affordable that I recommend reading them all 
Good luck and let us know how you get on!