What mistake did the chef make while preparing for the lunch buffet?

The mistake regarding the use of a steam table to reheat food is significant due to food safety standards. A steam table is designed to keep already cooked food warm and safe for serving rather than reheating it. When food is reheated, it should reach an internal temperature of at least 165°F quickly to kill any harmful bacteria that may have developed during storage. Steam tables typically do not provide sufficient heat to bring food up to this temperature quickly, increasing the risk of foodborne illness. Therefore, using a steam table for reheating food does not comply with best practices in food safety.

While the other choices present various food safety practices, they do not represent critical mistakes. For instance, proper handwashing is essential for preventing contamination, and a cooler being too warm would represent a different type of issue in food safety related to storage. Not washing hands after answering the phone touches on hygiene, but it does not align directly with the reheating and holding of food. The decision to use a steam table incorrectly highlights a crucial error in food handling procedures.