1. expand upon an existing level of success or achievement
build on a relationship/success/opportunity
When you ‘build on’ something you add to something that has already begun or is established; usually, something that is already successful or that has been achieved. You could ‘build on a relationship’ with your co-workers, or ‘build on an opportunity’. This is a common phrase used in social and business situations, but you are more likely to hear it used in a professional or formal context.