A remix of @bradgessler's Phlexable concern described here: https://fly.io/ruby-dispatch/hacking-rails-implicit-rendering-for-view-components/

phlexable.rb

# This concern will augment the default rendering behavior of a controller. If
# no matching view template is found for an action, a Phlex view will be
# searched for. First at a constant defined within the controller that matches
# the name of the action (`Edit`, `Index`, etc), and then within the views
# folder defined under `#{controller_name}::#{action_name}Page`
# (e.g. Admin::Bottles::IndexPage)
#
# If a matching Phlex view is found, it will be initialized with the defined
# instance variables that match it's own attributes (defined using the
# `attribute` macro).

module Phlexable
  extend ActiveSupport::Concern

  class_methods do
    def phlex_action_class(action:)
      action_class_name = action.to_s.camelcase
      return const_get(action_class_name) if const_defined?(action_class_name)

      "#{self.name.delete_suffix("Controller")}::#{action.to_s.camelcase}Page".safe_constantize
    end
  end

  protected

  # Phlex views define their attributes using the `attribute` method. If the
  # controller has an instance variable with the same name as the attribute, it
  # will be passed to the view as an argument.
  def build_phlex_initializer_arguments(phlex_view)
    needed_attributes = phlex_view.literal_attributes.keys

    needed_attributes.filter_map do |attribute|
      string_attribute = attribute.to_s
      [attribute, view_assigns[string_attribute]] if view_assigns.key?(string_attribute)
    end.to_h
  end

  # Initializes a Phlex view based on the action name.
  def phlex_action(action)
    phlex_class = self.class.phlex_action_class(action: action)
    return unless phlex_class

    arguments = build_phlex_initializer_arguments(phlex_class)

    phlex_class.new(**arguments)
  end

  # Phlex action for the current action.
  def phlex
    phlex_action(action_name)
  end

  # Try rendering with the regular Rails rendering methods; if those don't work
  # then try finding the Phlex class that corresponds with the action_name. If that's
  # found then tell Rails to call `default_phlex_render`.
  def method_for_action(action_name)
    super || if self.class.phlex_action_class action: action_name
               "default_render"
             end
  end

  # Renders a Phlex view for the given action, if it's present.
  def default_render
    render phlex, layout: false
  end
end