Use the mobile app as remote control for the web app

To give this some context, imagine this: You’re taking a nice bath, open plex web in your browser, fullscreen it, sit back, grab your phone to pick a movie and suddenly discover that you can’t select your laptop as the player to connect to.

Obviously you don’t want to have to get up every time you want to pick something different, and you shouldn’t have to. Look at spotify, I can control what plays on my PC from my phone, and vice-versa.

I’d really like an option in the web client settings where you can enable a feature to “advertise as player” so your phone, or different app, is able to connect to it (chromecast style) and control it.

This is already possible.
https://support.plex.tv/articles/categories/plex-apps/plex-companion/

Both the computer with the running web app and the phone must be connected to the same local network.
It might also be only possible if there is a running Plex server in this network, because the web app cannot open a port and listen on it. The security model of web browsers prevents it.

Instead of using the web app, install Plex Media Player. If you put it into ‘desktop mode’, it will look just like the web app. But it has more abilities than the web app.

Thanks, I’ll give that a shot

Early 2021 clean-up: implemented/possible