空港までのタクシーを予約したいって英語でなんて言うの？

Could you arrange is a polite request to do something. Arrange implying to book. I need a taxi asserts urgent nature of request. And do you offer a booking service is asking if it is possible to do something. In this case book a taxi. If answer is yes then arrangements can be made

"I would like to book a taxi for the morning to go to the airport.", can be used to express your desire for the staff to get a taxi booked for you so that you can get to the airport.

A polite way to start a request is to say: "Could you........?" The time tag is probably best placed at the end of the sentence: later today, at 4pm etc "Could we meet at 11am tomorrow morning?

In the first sentence, you explain what you need, which is a taxi. In the second sentence, you ask if the reception staff is able to book you a taxi. They should be able to do so but in case they cannot, they will give you information so that you can do so. I hope that this helps :)

By explaining to the hotel staff that you are in need of a taxi to go to the airport they will understand your urgency and importance of having one. Most hotels do provide that service. It is always better to add a please when requesting something from the hotel staff; that would show your good manners and respectfulness. Hope this helps!

I will be needing a taxi cab tomorrow morning at 8 to go to the airport. Can you book one for me? This is a common request especially at a hotel. In the form of a question is always more polite, also if any request starts with "would you be so kind as to...." it is both polite and kind, and more likely to have a positive reaction from the receptionist/concierge. Otherwise, "Please book me a taxi cab for tomorrow morning at 8 to go to the airport" is demanding, not rude, but not friendly either, and more similar to a command rather than a request.