How to know which is my current environment at Phoenix framework

If the MIX_ENV environment variable is empty Mix.env defaults to :dev:

$ iex -S mix
> Mix.env
# => :dev

If you set MIX_ENV to another existing environment (test or prod, then Mix.env will return it:

$ MIX_ENV=test iex -S mix
> Mix.env
# => :test

There's no need to define another config.

To get something from your config use for example Application.get_env/2:

Application.get_env(:your_app_name, YourAppName)[:adapter]
# => Ecto.Adapters.Postgres

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