The antonyms for the phrase "calling aloud" include "whispering," "muttering," "speaking softly," "hushing," and "whimpering." These words indicate a lower intensity of vocalization, and a more subdued and quiet way of communicating. Whispering and muttering are similar in that they both involve speaking in a hushed tone, but muttering is often associated with mumbling or talking indistinctly. Speaking softly implies a gentler and more soothing way of communicating, while hushing means to silence or quiet someone or something. Whimpering refers to a low, plaintive cry, often made in distress or pain. All of these antonyms convey a different way of speaking from calling aloud, which involves speaking in a loud, forceful manner.