If you’ve ever exchanged small talk with the cashier when checking out at a store, you’ve engaged in phatic communion. He says, "Hi, how are you?" and you say, "Great. Yourself?" and he replies, "Good. Hot out there today, isn’t it?"
Phatic utterances are not intended to tell the other person anything, get information from them, or issue a command. They’re just to share goodwill, to keep the social "wheels" turning smoothly and keep things from being stiff and awkward — like in an elevator where nobody talks for 17 floors. Often they're just the short remarks like "Serious?" or "Oh, my gosh!" that you insert when somebody’s talking to you, to let them know you’re listening with interest. Phatic comes from Greek phatos, meaning "spoken."