RTR(A) phraseology

Clearance

Start-up, ATC route clearance and the read-back each one demands.

Obtain ATC clearance

Used at the start of a flight, before pushback/taxi, when the pilot calls the appropriate ATC unit (here Tower, often Clearance Delivery at larger airports) to obtain the initial ATC clearance, the official authorization detailing the cleared destination, level, and departure routing the aircraft must follow. This must be obtained and read back correctly before the aircraft can be cleared to push back, start, or taxi, as it forms the basis for ATC's separation planning for the entire initial climb-out.

Pilot

[Station] [Callsign] [aircraft type] REQUEST ATC CLEARANCE

ATC

[Callsign] IS CLEARED TO [destination] AT [level] AFTER DEPARTURE [initial departure instructions: heading/altitude, turn/intercept instruction, intermediate level], THEREAFTER RESUME NORMAL NAVIGATION CLIMBING [final level]

Pilot

Delhi Tower, Akasa Air 1532 Heavy, request ATC clearance.

ATC

Akasa Air 1532, Delhi Tower, cleared to Mumbai via BUBKO FL300. After departure, climb runway heading to 2500, turn right, intercept radial 350 at 15 DME or less, climb to FL70, thereafter resume normal navigation, climbing FL300.

Pilot

Cleared to Mumbai via BUBKO FL300. After departure, climb runway heading to 2500, turn right, intercept radial 350 at 15 DME or less, climb to FL70, thereafter resume normal navigation, climbing FL300, Akasa Air 1532.

"Request ATC clearance" is a standalone, simple request, no additional information (position, intentions, etc.) is needed since the aircraft is on the ground at a known location (its parking stand/gate), and the flight plan is already on file with ATC.
The clearance given is a full SID-style departure clearance even though specific named SID waypoints aren't used here, instead it's a procedural/vector-based departure: runway heading to an altitude, then a turn to intercept a specified radial at or before a DME distance, climb to an intermediate level, then resume own navigation (i.e., proceed per the flight plan route) while continuing to climb to the cleared cruise level.
Cleared level (FL 300) is the cruise clearance limit, "climbing FL 300" at the end confirms the aircraft is cleared to climb all the way to FL 300 as part of this clearance, not just to the intermediate FL 70.
The structure follows the standard order: destination and cruise level → departure instructions (initial heading/altitude → turn/intercept instruction → intermediate climb level) → "thereafter resume normal navigation" → final cleared level for the climb.
This clearance must be read back in full by the pilot, a partial or incorrect readback is one of the most common sources of error tested in checkrides/vivas, since ATC relies on the readback to catch any misunderstanding before the aircraft moves.
"15 DME or less" gives the pilot some flexibility in exactly where the turn occurs (any point up to 15 DME), but the turn must not be delayed beyond that distance, useful for the pilot to manage the turn in conjunction with the climb to 2500.
Once this clearance is read back correctly and acknowledged, the next step is normally requesting pushback/start (a separate transmission), not departure itself, clearance delivery and takeoff clearance are distinct stages.
If anything changes before departure (route, level, etc.), ATC will issue an amended clearance, and the pilot must read back the changes again.

Reference: ICAO Doc 9432

Reading back a route clearance

When ATC issues an IFR route clearance before or during taxi.

Pilot

{CALLSIGN}, request clearance to {DESTINATION}.

ATC

{CALLSIGN}, cleared to {DESTINATION} via {ROUTE}, initial climb {LEVEL}, squawk {CODE}.

Pilot

Kolkata Ground, Skyline 345, information Alpha, request clearance to Delhi.

ATC

Skyline 345, cleared to Delhi via filed route, initial climb four thousand feet, squawk two one zero seven.

Pilot

Cleared to Delhi via filed route, initial climb four thousand feet, squawk two one zero seven, Skyline 345.

ATC

Skyline 345, readback correct.

Write the clearance while it is passed slowly, then read back destination, route, initial level and transponder code.
A route clearance is not permission to start, push, taxi, enter a runway or take off.
Wait for the controller to confirm the readback before treating the clearance as accepted.

Reference: ICAO Doc 9432, 2.8.3

Request ATIS

Used to request the current Automatic Terminal Information Service when the pilot has not yet been able to copy it from the dedicated ATIS frequency. The ATIS letter (Alpha, Bravo, Charlie...) identifies the broadcast version so the pilot doesn't quote stale information.

Pilot

[Station] [Callsign] REQUEST ATIS

ATC

[Callsign] INFORMATION [letter] CURRENT [or full ATIS read-out]

Pilot

Delhi Ground, Akasa Air 1532 at Stand 24, request ATIS

ATC

Akasa Air 1532, Delhi Ground, information Bravo current, runway 29 in use, wind 270 at 7 knots, QNH1013

Pilot

Information Bravo, runway two niner, wind two seven zero seven, QNH one zero one three, Akasa Air 1532

Always state the ATIS letter you have copied on first contact (e.g. "information Bravo") so ATC can confirm or update.
If the ATIS letter has changed since you copied it, ATC will pass the differences only, listen for them.

Reference: ICAO Doc 9432

Request Departure Clearance (IFR)

Used by IFR flights to obtain the airways clearance before pushback. The clearance contains the route, initial level, expected level, departure procedure, transponder code, and any specific instructions.

Pilot

[Station] [Callsign] STAND [number] REQUEST CLEARANCE [destination] INFORMATION [ATIS letter]

ATC

[Callsign] CLEARED TO [destination] VIA [route], [SID], CLIMB [initial level], EXPECT [final level] [time], SQUAWK [code]

Pilot

Delhi Delivery, Akasa Air 1532 Stand 24, request clearance Mumbai information Bravo

ATC

Akasa Air 1532, Delhi Delivery, cleared to Mumbai via DURGA1A departure, BUBKO, flight planned route, climb 5000 feet, expect FL320 10 minutes after departure, squawk 5271

Pilot

Cleared to Mumbai via DURGA1A, BUBKO, flight planned route, climb 5000 feet, expect FL320, squawk 5271, Akasa Air 1532

Read back the entire clearance verbatim, route, SID, initial level, squawk. ATC will issue "readback correct" once satisfied.
If the clearance is lengthy, write it down before pressing PTT to read it back.

Reference: ICAO Doc 9432

Requesting start-up

Before starting engines after receiving departure information.

Pilot

{UNIT}, {CALLSIGN}, {STAND}, request start up, information {ATIS}.

ATC

{CALLSIGN}, start up approved, QNH {QNH}.

Pilot

Bengaluru Ground, Skyline 345, stand three four, request start up, information Bravo.

ATC

Skyline 345, start up approved, QNH one zero one zero.

Pilot

Start up approved, QNH one zero one zero, Skyline 345.

State your location or stand and acknowledge the current ATIS information letter.
ATC may approve immediately or give a start-up time. Write down the exact time if one is given.
A start-up approval does not authorize push-back, taxi or runway movement unless those are separately given.

Reference: ICAO Doc 9432, 4.2