As eyeinthesky states, the phrase "Cleared to enter control zone" i incorrect.
The readback to "O-BC Enter (or cross) controlzone and report final rwy 27" is simply:
"Entering (crossing) controlzone and report final rwy 27, O-BC)"
eyeinthesky was making the opposite point, that the ATCO
should have offered a clearance, not simply an instruction.
The readback you suggest is misleading for a different reason: "Entering control zone" sounds like a position report. The instruction (or preferably clearance
) may be given with the aircraft 20 miles away.
Finally, reporting instructions should not be read back.
(All of this applies in the UK and under ICAO PANS-ATM. Denmark may have different rules, but I doubt it.)