Final answer:
The phrase is best described as a mission statement, which is meant to define the purpose and direction of an organization.
Step-by-step explanation:
The phrase 'To participate as the air component of the MAGTF...' is best described as a mission statement. A mission statement is designed to provide a purpose and direction for an organization or group. It generally outlines what the group is to do and sometimes how it should do it, focusing on the present. This contrasts with a vision statement, which articulates a future goal, and core values, which guide the behavior and decision-making processes of the organization's members.