That's how my LG TV works. The TV shows up in the cast menu just like a chromecast does. Using youtube as an example, it opens up the youtube app and starts the video. You can either use the remote as usual to interact with the video, or the you phone exactly like you would if it were just a chromecast. You can also queue up multiple videos from your phone.

I have a chromecast as well, and I really expected to use it over the built-in apps. But the built-in TV apps really blew me away, much better user interface than I was expecting. I'm hoping this new chromecast/Google TV thingy is as good, I'd really like to disable network connectivity to the TV if possible (but right now the apps are just too nice to give up).