just created a new phx app from scratch and copy pasted in your code. For me it worked fine (also the broadcast from the controller). I can see all messages inside the browsers dev console.
The only change on top of your code was uncommenting this line in app.js:
import socket from "./socket"
with these kind of issues I would advise to create a public github project with your whole project inside, in that way people can help you better and you talk about the exact same code (bit by bit).
