Wouldn't it be better to prepare the shopping list instead of dialing home to ask which salad to buy.

dialing 是动词 dial 的现在分词形式。dial 本意是指"拨号"，因为老式电话需要拨动转盘来输入号码，后来引申为"打电话"的动作。在句中 dialing home 表示"往家里打电话"的意思。