Final Answer:
The nurse responds first to the phone message from the parent of an adolescent reporting that the child threatens self-harm with access to a gun.
Step-by-step explanation:
In prioritizing phone messages in an outpatient clinic, the nurse must consider the urgency and potential risk to the patient. The situation described in message 1, involving an adolescent threatening self-harm with access to a gun, is a critical emergency that requires immediate attention. This situation poses an imminent risk to the patient's safety, and the nurse should initiate emergency response protocols, involving law enforcement or crisis intervention teams as necessary. The other messages, while important, do not present an immediate and life-threatening situation. Timely and appropriate intervention in the case of self-harm threats is crucial for patient safety.