The phrase "whistle stopped" has a number of synonyms that can be used in its place. One alternative is "halted," which means to come to a stop. Another synonym is "terminated," which indicates an end or conclusion. "Ceased" is another option, which denotes the cessation of an action or motion. "Interrupted" is another synonym, which suggests the interruption of a flow or continuity. Lastly, "paused" is a synonym for "whistle stopped," which suggests briefly stopping an ongoing activity or motion before resuming. These synonyms can be used interchangeably with "whistle stopped" to add variety and depth to a sentence or phrase.