There are several synonyms for the phrase "stop talking." One common option is "be quiet," which is often used when someone is being too loud or interrupting others. "Shut up" is a more forceful and aggressive way of telling someone to stop talking, and is generally considered impolite. "Silence" can also be used, though it is less commonly used in conversation and more often found in written instructions or commands. Another option is "cease speaking," which is a more formal and elegant way of expressing the same idea. Ultimately, the choice of synonym depends on the specific situation and desired tone.