That's because "Rails with performance" was one of Phoenix's selling points from day one, Phoenix was inspired by Rails and Elixir is heavily influenced by Ruby

That's because "Rails with performance" was one of Phoenix's selling points from day one, Phoenix was inspired by Rails and Elixir is heavily influenced by Ruby, prior to 1.3 killing the models in favor of contexts Phoenix contained an extremely similar structure to Rails MVC with less implicit conventions.