it comes down to context whether it is a phrase or a sentence, because 'is' is nonexistent in Arabic. As such it is perceived differently.

If said independently like someone just says 'Sam jadeed' it means 'Sam is new' (like introducing Sam on the first day of the job to Sam's peers)

If it is within context as in answering a question (like the example stated), then it can be a phrase as part of a sentence "No, he is 'a new Sam' "

It may be clearer once definites are clearer because if a definite addition is made, the meaning and structure changes.