Final answer:
The first nursing action should be to direct the client with bipolar disorder in the manic phase to their room for a time-out, ensuring the client's and others' safety while providing a chance for de-escalation.
Step-by-step explanation:
When dealing with a client with bipolar disorder in the manic phase who is exhibiting aggressive behavior, the priority is to ensure the safety for the client as well as others present. In this scenario, the client is yelling, has a flushed face, and clenched fists, which could escalate to violence. The first nursing action should be C. Direct the client to his room for a time-out. Directing the client to a quieter, private space can help de-escalate the situation and provide an opportunity for the client to regain control without the need for physical intervention or immediate medication administration. This action also respects the client's dignity and provides a less restrictive alternative. After the client is in a safe environment and calmer, further assessment and interventions such as discussing the problem or medication may be considered.