The Igniter installer configures Phoenix development HTTPS and stores the browser URL in application config:

config :my_app, MyAppWeb.Endpoint,
  url: [scheme: "https", host: "my_app.test", port: 4001],
  https: [
    port: 4001,
    cipher_suite: :strong,
    keyfile: "priv/cert/selfsigned_key.pem",
    certfile: "priv/cert/selfsigned.pem"
  ]

config :star_view, dev_url: "https://my_app.test:4001"

The installer also queues:

mix phx.gen.cert my_app.test localhost

That gives the generated Phoenix certificate a subject alternative name for the local .test host used by mix dev.

Starting Phoenix

Run:

mix dev

mix dev delegates to:

mix star_view.server

mix star_view.server starts mix phx.server --open, so Phoenix opens the configured endpoint URL. Pass --no-open when you want to start the server without opening a browser:

mix star_view.server --no-open