There are many synonyms that can be used instead of the phrase "line up." Some possible options include "queue up," "form a row," "get in formation," "stand in order," "arrange in sequence," "marshal into place," "organize in a line," or "assemble in a column." These phrases all convey the idea of people or objects being arranged in a straight, orderly fashion. Depending on the context, different synonyms might be more appropriate or convey different nuances of meaning. For example, "queue up" can suggest waiting in line for a service or product, while "get in formation" can connote military or athletic activities.