Which phrase correctly indicates the altitude to "check-in" for a rendezvous with Sidewinder 204?

The phrase that accurately indicates the altitude to "check-in" for a rendezvous with Sidewinder 204 is “Passing Angels 2.5 CHECK IN BUTTON 2.”

In aviation communication, "Angels" is a standard term used to describe altitude in thousands of feet. Therefore, "Angels 2.5" translates to an altitude of 25,000 feet. The use of “CHECK IN BUTTON 2” specifies the designated radio frequency or communication channel for this particular check-in, ensuring clarity among the pilots and air traffic control.

This particular combination of altitude and check-in button is essential for maintaining organized communication during the rendezvous. It reflects clear coordination and situational awareness, which is vital in air traffic control operations. The specificity of altitude and the chosen check-in button are critical components in enabling safe and effective interactions in busy airspaces.