You need an app on your phone that “flings” the content from the NAS, so a media server like Jellyfin.

My bad, i was unclear. I don’t think chromecast can source NAS. In my experience you can stream to chromecast via a device player, like VLC.

WebOS can also play files direct from a NAS though, but that obviously involves downloading in full to the NAS before playing.

I suppose it can source the NAS directly using something like DLNA protocol