data_live.ex

defmodule FoldlaWeb.DataLive do
  use Phoenix.LiveView

  def render(assigns) do
    FoldlaWeb.DataView.render("edit.html", assigns)
  end

  def mount(_params, socket) do
    {:ok, assign(socket, :thing, 0)}
  end

  def handle_event("inc", _value, socket) do
    {:noreply, assign(socket, :thing, socket.assigns.thing + 1)}
  end
end

edit.html.leex

<span phx-ignore>Here is the thing: <%= @thing %></span>

phoenix: "~> 1.4"
phoenix_live_view: github: "phoenixframework/phoenix_live_view"
View layout: default

This!