I'd probably question if this is even possible in a healthy individual. You probably eat a lot of phenylalanine regularly. My intuition is that you'd really have to go out of your way and actively want to give yourself brain damage to even achieve this.

Given this: https://www.myfooddata.com/articles/high-phenylalanine-foods... which shows chicken breast has 2190mg and your average can of diet coke has around 104 mg https://pubmed.ncbi.nlm.nih.gov/1617863/, I think that probably holds.

EDIT: That link probably underscores that the warning label on your coke can is purely for the benefit of Phenylketoneurics, not you. A steak & 2 egg breakfast with a latte would land you with far more phenylalanine than you could sanely consume purely through coke. You'd likely be sick from the caffeine sooner than the phenylalanine.