If I understand correctly you have one root and 2 layout lets call them app(the original) and admin

To decide with Live View will be using which layout you need to edit your MyappWeb.ex

The original is as follow, keep it as it is

def live_view do
    quote do
      use Phoenix.LiveView,
        layout: {MyappWeb.Layouts, :app}

      unquote(html_helpers())
    end
  end

Create a new one under

def live_view_admin do
    quote do
      use Phoenix.LiveView,
        layout: {MyappWeb.Layouts, :admin}

      unquote(html_helpers())
    end
  end

and then in your Admin Live View you do

  use MyappWeb, :live_view_admin