There are a number of different phrases that could be used as synonyms for the phrase "sucks up to." Some of the most common might include "brown-noses," "kisses up to," "flatters," "crawls," or "grovels." All of these phrases can be used to describe someone who is trying to curry favor with another person, often in a way that involves insincere or excessive flattery. While it's always important to be polite and respectful when dealing with others, it's important to avoid going overboard in an attempt to win someone's approval or favor, as this can often backfire and lead to mistrust or resentment.