How much phenylalanine?

Aspartame: "In the synthesis of aspartame, the starting materials are a racemic mixture (equal quantities of both isomers) of phenylalanine, and aspartic acid."

So, about half. And Diet Pepsi contains about 124 mg of aspartame per 355 ml bottle. That makes it about 62 mg of phenyalanine per 11.8 ounce bottle. A big refillable cup of about 32 ounces then would net you about 180 mg.