The phrase "pipe down" is commonly used to tell someone to be quiet or stop talking. However, there are several other synonyms that can be used in its place. For instance, "hush," "shush," and "quiet" all have similar meanings to "pipe down." Additionally, "be quiet," "zip it," and "button it" can also be used to tell someone to stop talking. Other phrases such as "silence please," "shut up," and "not a word" can also convey the same message. These synonyms can be used interchangeably, depending on the context and situation, to express the need for someone to stop talking or be quiet.