Muffle up is a phrasal verb that is commonly used to refer to the act of wrapping or covering oneself or something else with a warm garment to keep away from the cold. However, there are few other phrases that can be used interchangeably with muffle up. Some of them are bundle up, wrap up, cover up, and snuggle up. These phrases are all similar in the sense that they refer to using a garment to protect oneself or others from the cold. They are often used in the context of winter activities and are an essential part of maintaining one's health and comfort during cold weather.