To use IEx.pry to break into simple debugger for your Phoenix app you need to require IEx first and then you can invoke IEx.pry within a function to create a break point. When the debugger breaks you can then view the data structures previously declared.

Note: This is pretty limited as you cannot step through code etc. like you can with most other debuggers. Note: you need to run your app with: iex -S mix phx.server and you must require IEx.

require IEx

    data = %{ data: %{status: 200} }
    IEx.pry

See the following blog post for more details including how to debug templates.

Links:

Debugging Phoenix with IEx.pry