The Question and Answer section for The Road is a great resource to ask questions, find answers, and discuss the novel.
While at the gas station, the father picks up the phone and called what used to be his father's number. We can infer that he was reaching out to the past.... and remembering and wishing for an answer.
The father's flasbacks inform the reader of exactly how he and the boy ended up on the road alone, together, and without his wife. The flashbacks provide us with a back story.
My copy has pg 278 but there are many probably many different publications of this book.