Are you talking about screen mirroring, so you can see and hear it through the phone, that is the only way I know of. There is no way to just use the phone as a speaker.
NOTE: Your TV must be capable of doing this as well. So you will need to check the TVs info.
How to use "Screen Mirroring" with an S6 and a Samsung TV.
(If you have a different brand of TV then you will need that TVs info to get the connection right.)
Connecting to a TV
First you need to register/connectr a TV to your device. Once you register/connect the TV, you can easily share the screen between your device and TV and use the Briefing on TV feature.
1. Turn on the TV and place your phone close to the TV.
2. Open the notification panel and tap "Quick Connect"...