Thank you. I tried “###,###” (which was immediately converted to “#,###”) as well as “#,##0”. Both of these resulted in what seemed to be the required format e.g. 3,048.
SELECT Call8PointInfoQry.電話番号(MSN), Sum(Call8PointInfoQry.PointsNumber) AS PointsNumberOfSum, Format([PointsNumber],"#,###")...