The phrase "in quantity" can be replaced with a variety of synonyms depending on the context in which it is used. Some commonly used synonyms include "in bulk," "in abundance," "in large numbers," "in great quantities," "en masse," "in profusion," "extensively," "lavishly," "copiously," "in excess," and "in droves." These synonyms can enhance the language and make it more descriptive and specific to the situation or topic being discussed. It is important to choose the most accurate synonym to effectively convey the intended meaning of the sentence.