Ideally, all phone conversations and meetings should be followed up with a confirmation to ensure there is a record of the decisions made and action points agreed upon. It is essential that meetings and phone calls are prepared for adequately to ensure they are conducted efficiently. However, the reality often is that after a meeting or phone call, we immediately move on to the next task at hand. Therefore, the following workflow is recommended:
Figure: Confirm decisions and action points throught an "as per our conversation" email
"No plan survives first contact with the enemy" is a popular saying for a reason. Your draft email should moslty just be bullet points to make sure you don't forget to mention anything you had planned to.
You'll refine and beautify it after the conversation.