The phrase "builds upon" can be replaced with synonyms such as "expands on," "develops further," "extends," "elaborates on," "advances," and "enriches." Each of these expressions convey a sense of progression, growth, and enhancement. When used in writing or speaking, they can convey a sense of expertise and mastery of a subject matter. For example, a teacher who elaborates on a difficult concept, or a researcher who advances a new hypothesis, are both building upon existing knowledge and pushing the boundaries of what is known. Choosing the right synonym for "builds upon" can enhance communication and add nuanced meaning to your writing or speaking.