I remember that when I was taught the phatic function of language, it was a minor epiphany. Prior to that, I thought of small talk (nice weather today, how was your weekend, how about those Broncos) as meaningless bullshit, which was really a problem for me. That concept made me understand that it isn't meaningless, it just has a different kind of meaning than referential language does (which really would be about the weather). Phatic language is about maintaining the connection. It communicates, "I think you're worth communicating with, you're an acceptable interlocutor" and so on. It's used most often with people one doesn't know well because it signals reduced risk. Without it, people feel tense and suspicious. No doubt there are deep-seated reasons for this.

But that doesn't at all mean that it should play the same role in writing.