Does "number noun" phrase require hyphenation?

Here is my sentence:

I have written a five page article.

Is the above sentence correct? Or does it need to be hyphenated like this?

I have written a five-page article.

Is there a name for the grammatical concept of using a "number noun" phrase like this as an adjective for another noun? For example, here "five page" acts like an adjective for the noun "article". What grammatical term is there to refer to such phrases? I am asking this because if I had known the term, it would have helped me to perform Google search to find the answer to my question.