"Fell in line" is an idiomatic expression that refers to the act of conforming to a certain group or following a certain set of rules or beliefs. A few synonymous phrases for "fell in line" include "fall in step with," "comply with," "fall in line with," "conform to," "adh ere to," and "abide by." These phrases can be used interchangeably in various contexts, such as in the workplace, schools, and societal organizations. They all express the importance of following instructions or rules and cooperating with others to achieve a shared goal. In essence, they imply a sense of agreement or alignment with a particular group or idea.