You can add as many portfolio items to your profile as you can. As long as you only use projects that you personally contributed to (for example don’t use a project by somebody else even if they are in the same agency) and that meet Upwork’s Terms of Service. You may want to check this help article to learn more about enhancing your profile.
Thank you for reaching out to us. Your portfolio should contain written and visual overviews of projects and pieces of work that you've managed or been involved with. If this was a personal project, you may add it to the "Other Experiences" section of your profile.