How should I ask for a raise?

My department recently got a huge investment for a new project that me and one other employee essentially did the development for. This other employee has been out of town the past three weeks, so I have been doing all their work along with mine.

Found out yesterday this person is quitting effective immediately and I know I will be working way harder/a lot more for this project as a result. I feel I should be compensated appropriately.

I do have leverage as I will be the only one with the skills needed to do this work.

Also, I have been working here for over five years. Each year I get the token 3% raise.

I just wonder what you guys think is the best way to phrase things? I can be pretty direct and obtuse sometimes (possible autism).