Phoenix is written in Elixir, so definitely not a 1:1 mapping, but because of the underlying BEAM VM, most of what makes Elixir robust should in theory also apply to Erlang. Apart from OTP which is amazing, I don't know anything at all about the Erlang web framework scene though, sorry.
OTP predates Elixir and stems from the creation of Erlang. The only real difference between the two is that Elixir has a nicer syntax and some higher level abstractions.
