The phrase "becomes narrower" can be substituted with various synonyms to add more specific meaning to a sentence. Words such as constricts, tightens, shrinks, tapers, and thins can be used to describe something that becomes narrower. The term constricts implies a gradual decrease in space, while tightens suggests something that is becoming restrictive. Shrinks is used when something decreases in size, and tapers refers to a gradual decrease in size from one end to another. Finally, thins describes a state where something becomes slender or lean. Choosing the correct synonym for "becomes narrower" can help to clarify a sentence and add more depth to the overall meaning.