A phrase has at least two words
The truth/falsity of this part of the sentence depends on definition. That means that if you think having more than one word is a definitive requirement of phrases, then it's true. If you don't accept such a requirement, then it's false.
so a pronoun can not be a Noun Phrase.
This is a logical conclusion of the premise of the first part of the sentence. So if you define phrases as necessarily having more than one word, then it's true. But if you don't, it's false. But the logic only works as long as the word 'phrase' is being used with the same definition in each clause.
So whether it's true or false depends on your definition. I think most grammarians these days find it more useful to define phrases in such a way that includes single words.