O Elixir School é bem legal! Depois de passar por ele, recomendo os materiais abaixo:
https://www.udemy.com/course/elixir-e-phoenix-do-zero/
https://www.udemy.com/course/the-complete-elixir-and-phoenix-bootcamp-and-tutorial/
https://pragprog.com/categories/elixir-phoenix-and-otp/
Abs.!