Here's why:
* Phrase: A group of related words that does not have a subject and verb working together to form a complete thought.
* Clause: A group of words that contains a subject and a verb and expresses a complete thought.
Let's look at some examples:
* Phrase: "Running through the park" (Subject: missing; Verb: "running")
* Clause: "The dog ran through the park." (Subject: "dog"; Verb: "ran")
A phrase can be used as part of a sentence, but it cannot stand alone as a complete sentence.