Final answer:
The best course of action is to excuse yourself from the guest and answer the phone in order to provide good customer service.
Step-by-step explanation:
When the phone rings while you are helping a guest, the best course of action is to excuse yourself from the guest and answer the phone. It is important to address the call promptly to provide good customer service. However, it is also important to let the guest know that they are valued, so it is polite to apologize for the interruption and reassure them that you will assist them as soon as you finish the call.