However, it's important to note that this phrase is almost never used in everyday French conversation. It's a very formal and awkward way to say that someone has three of something.
The more common and natural way to say "He has three" in French is "Il a trois [noun]."
For example:
* "Il a trois livres." (He has three books.)
* "Il a trois enfants." (He has three children.)
It's also possible that you're thinking of the phrase "il y a trois," which translates to "there are three."
So, depending on the context, "il a trois" can be interpreted as a grammatically correct but very formal way to say "he has three," or it might be a typo for the more common phrase "il y a trois," meaning "there are three."