Fill someone's shoes is a figurative expression that means to take over someone's position or role. There are several synonyms that can be used in place of this phrase, such as step into someone's shoes, assume someone's responsibilities, inherit someone's job, or take on someone's mantle. All of these phrases denote the idea of taking on the responsibility and duties of someone who has left a particular position. These synonyms can be used in various contexts, including the workplace, family, or social settings, and can be used to express empathy, admiration, or encouragement for someone taking on a new role.