I think the chatgpt thing is a good draft, maybe you have to do some improvements to do.
With node.js you can create a backend server, that gives a rest-api for communicating with your db. Phones can call this rest-api to update the counter and your big screen can fetch in a given intervall, from your backend server to give a live-update. (This concept is called AJAX) Make sure to track session IDs and maybe some sort of uuid to ensure every phone can give only one vote on each decision and to relate the phones to the correct big screen. (If you want that multiple games can be done simultaniously)
Express is just a node.js Framework so you haven't to write that much code on your own.
If something is unclear do not hesitate do ask, I will update the answer.
But please keep in mind that SO is not the place to give you hundreds line of code, so you do not have to write them at your own. If you have a problem with your code, make a new question, post a minimal example, that reproduce the error. Describe what it should do, what you have tried to solve it, etc.