Built upon is a phrase that describes the process of taking something as a foundation and developing it further or adding to it. For instance, someone can build upon an idea, thought, or an existing structure. The phrase is commonly used in business, science, and technology. Some synonyms that can be used instead of "built upon" include expanded upon, elaborated on, augmented, progressed, enhanced, improved upon, grown, and developed. These words all convey the same meaning as "built upon," and can help vary language and avoid redundancy. It is important to use synonyms carefully to ensure that the intended meaning is not lost in translation.