This is a really really bad comment. I've never heard of the framework you're talking about and I thought you were talking about the Firefox prototype.
Phoenix is a well known web app framework regardless of your ignorance of it.
If you’re in software dev or frequent hn, how have you not heard of Phoenix? It is consistently voted as most loved web framework.
I don't have an opinion on the matter, but it's pretty popular. According to [1], Phoenix "was used extensively over the past year" by 2.4% of responders.
[1] https://survey.stackoverflow.co/2025/technology