There are a number of conflicts in "A Small, Good Thing," as is the case with most stories, but when we think about which is central to the narrative, it's fairly clear that the loss of Ann and Howard’s only child is the dominant struggle. The couple is situated in the story as leading protagonists and the main conflict they face is Scotty’s car accident and consequent death. The accident introduces the explosive force of uncontrollable and arbitrary events into the couple's previously intact and unblemished lives. Howard reflects on this when he returns home from the hospital on the night of the accident.
"Until now, his life had gone smoothly and to his satisfaction-college, marriage, another year of college for the advanced degree in business, a junior partnership in an investment firm. Fatherhood. He was happy and, so far, lucky-he knew that. His parents were still living, his brothers and his sister were established, his friends from college had gone out to take their places in the world. So far, he had kept away from any real harm, from those forces he knew existed and that could cripple or bring down a man if the luck went bad, if things suddenly turned.”
However, what's interesting about conflict as a literary device in "A Small, Good Thing" is that the baker poses an additional minor conflict throughout the story that stays in the back of the reader's mind, creating another layer of tension to the couple's situation. At first the fact that Ann never picks up Scotty's birthday cake seems completely trivial and unimportant to the bigger picture of the story, but the baker's mysterious phone calls, which repeatedly plague the couple when they are at home, keeps it in play as a minor dilemma in the narrative. We don't understand why Carver would make the baker and the birthday cake such a continuous source of tension in the story, especially when it's unrelated to the major conflict of Scotty's accident.
That's until the climax of the story when Ann and Howard decide to drive to the bakery to confront the baker. It's strange that the climax of the story should be the couple going to resolve this minor conflict. Their hatred and anger at the baker seems misplaced and the baker's offense of harassing them with phone calls is negligible compared to Scotty's accident. But then we discover that the couple's experience of going to the bakery actually becomes mainly about resolving the major conflict of their son's death, rather than the minor conflict of the baker's harassing phone calls.
So although the major conflict of "A Small, Good Thing" is Scotty's accident, Carver mixes in the minor conflict of the couple's fight with the baker, and we discover how the resolution of minor conflicts can also lead to the resolution of major conflicts. As the title suggests, "small, good things" like the couples union with the baker have larger impacts on the protagonists' ability to solve the major conflict they face.