You should ______ your phone call with an email or a letter.

Correct option is B

The correct phrase is follow up, which means to continue or reinforce a previous action or communication. In this context, it suggests confirming a phone call with written communication for clarity or record-keeping. For instance:
· "You should follow up your phone call with an email to ensure your message is understood."
Information Booster:
1. Follow up is essential in professional and personal communications.
2. Ensures actions or messages are completed or clarified.
3. Often used in contexts like business communication, medical care, and education.
4. Different from follow on, which implies continuation without reinforcement.