Literature isn’t meant to be a transcription of real life. Instead, it focuses on one aspect in order to illuminate something important. To create this focus, we have to exclude what isn’t necessary. So we cut out commutes, bathroom visits, and weekly trips to the bank in favor of those moments that reveal something about the story we’re trying to tell. The same is true for exchanges of dialogue. Those pleasantries that often happen at the beginning and end of conversations are commonplace. They often don’t reveal much. And they’re boring. If they’re not accomplishing anything, there’s no need to include them.
A story doesn’t lose reality because these pleasantries aren’t included. Rather, it keeps the pacing swift, and lets the reader focus on what is important about the conversation. Take measures to make sure the dialogue you do include sounds natural and convincing. That will create all the realism you need to make the scene authentic.