Phoenix relies heavily on Elixir macros, so you'd first have to compile and then try to call the generated functions... But I'm not sure that makes a whole lot

Phoenix relies heavily on Elixir macros, so you'd first have to compile and then try to call the generated functions... But I'm not sure that makes a whole lot of sense as you'd be missing out of most of the benefits of Phoenix. A more pragmatic approach is to use Elixir for the Phoenix specific parts, and from there call the other Erlang based languages for your business logic.