Antonyms for the phrase "lifted up voice" include, but are not limited to, "soft-spoken," "whispered," "muted," "hushed," and "murmured." These antonyms convey a sense of quietness and gentleness, as opposed to the strong and forceful nature of a "lifted up voice." Other antonyms such as "calm," "composed," "serene," "tranquil," and "composed" also indicate a sense of serenity and peace. These antonyms can be useful in situations where one wishes to communicate with subtlety and tact or convey a sense of calm and tranquility.