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 has a subject and verb working together, but it may or may not express a complete thought.
* Sentence: A group of words that has a subject and verb working together to express a complete thought.
Examples:
* Phrase: "Running through the park" (has a verb "running" but no subject)
* Clause: "When I go to the store" (has a subject "I" and verb "go" but doesn't express a complete thought)
* Sentence: "I went to the store." (has a subject "I" and verb "went" and expresses a complete thought)