It means "gradually refactor and gradually pack code in React/Angular components".

>> How big is the application? Yeah its pretty big. Has at least 7-8 different pages and workflows.

>>Does it have clear architecture and clean code or is it big ball of mud with ugly looking code?

The code is in "somewhat" good state. Few components we have followed MVC using vanilla js; where as few components still remain the same ( as ugly looking code )