There are several synonyms for the phrase "kiss up," which is generally used to describe someone who seeks to gain favor from someone else through flattery or sycophancy. Some of the most common synonyms include "brown-noser," "bootlicker," "suck-up," "toady," "apple-polisher," and "brown-nose." These terms all suggest someone who is insincere in their attempts to curry favor and may be seen as disingenuous or even manipulative. Other phrases that can be used to describe this behavior include "butter up," "flatter," and "pander to," although these are not necessarily as negative in connotation as some of the other synonyms.