Utterances that provide information are said to have a referential function.
For example: an announcement at a train station.
Utterances that are said to have an expressive function if they express the speaker's feelings.
These are verbal exchanges in which the main emphasis is on getting something done.
For example: asking for directions.
Here, the main emphasis is on the social relationship between the participants.
For example: speaking to someone who you have not seen for a while.
This is the technical term for "small talk". Utterances such as "Hello" or "Turned out nice again hasn't it?" are phatic.
Conversations often begin with phatic exchanges. They play an important role in establishing and maintaining social relationships.