ATC will use the phrase “while in controlled airspace” in conjunction with the altitude if an aircraft will be entering or leaving controlled airspace. In addition, ATC will specify the lateral point and altitude at which an aircraft is to leave or enter controlled airspace if the instruction is required for separation purposes (see Note).
Example:
LEAVE/ENTER CONTROLLED AIRSPACE 12 MILES NORTH OF YOW VOR AT 7,000 feet.
LEAVE/ENTER CONTROLLED AIRSPACE AT 3,000 feet.
NOTE: The altitude assigned by ATC need only reflect the minimum safe IFR altitude within controlled airspace. A pilot should be alert to the possibility of a higher minimum safe IFR altitude outside of controlled airspace. If uncertain (or unable to determine) when to enter or leave the area where the higher minima is applied, a request for clearance to maintain an altitude that will accommodate the higher minimum IFR altitude should be made.
REFERENCES AIM RAC 8.8 Clearances - Leaving or Entering Controlled Airspace