Is while you were talking on the phone to Walter a fragment?

Yes, "while you were talking on the phone to Walter" is a fragment.

Here's why:

* Missing a subject: It lacks a subject, the person or thing performing the action. Who was doing something "while you were talking on the phone to Walter"?

* Incomplete thought: The phrase doesn't express a complete thought. We need more information about what happened *while* the phone call was taking place.

To make it a complete sentence, you could add a subject and a verb:

* Example: "While you were talking on the phone to Walter, I finished the dishes."

Let me know if you'd like to practice with other sentence fragments!