“Since I did most of the work for the project, I would really appreciate if someone could take over my portion of the speaking. I’m not comfortable speaking in front of many people so I think it’s a fair trade.” Something like this could work OP. Your stance is strong while also being kind and appreciative. No one will say no. (Coming from someone who did this all the time in college - there was always at least one person in the group who would agree.) best of luck and stay strong OP!