That’s true, as far as it goes, but the amount of phenylalanine created is incredibly minute and is matched by other, “natural” foods. In the vast majority of people, the body quickly metabolizes excess phenylalanine. The only genuinely well-documented danger is for people with phenylketonuria, because they have a genetic variation that breaks that ability to metabolize.

Last I checked, which was admittedly years ago, the studies that showed direct harms were flawed, not statistically significant, or have not been repeatable. The early studies that led to its ban in the EU used absolutely massive doses of aspartame, well beyond what you could possibly ingest in a day.

I’m not saying it’s safe for sure but it’s safer than obesity or massive doses of sugar on a regular basis.