Final answer:
In this situation, the nurse should contact the nursing supervisor for assistance.
Step-by-step explanation:
In this situation, the most appropriate action for the nurse to take would be to contact the nursing supervisor. If the nurse is unable to reach the healthcare provider to clarify the illegible medication order, it is important to involve a higher authority who can provide guidance and assistance. The nursing supervisor can help in determining the best course of action, whether it's finding an alternative method to contact the healthcare provider or obtaining further instructions.