Polycarp

I think he is mentioned so as to set the scene and I think that it is also to compare him to Herr Resch to show how both of them do not do much just sit at home and occasionally call to conduct his business.

I believe that he is also there to like set the scene and that there would be something to occupy his attention and prevent him from seeing Friedrich once he got out from the air-raid shelter at the end of the story.