If you are going to order the taxi by phone, the sequence is the following: you call the telephone number, you tell a point of departure and arrival, you ask about the price or the operator says that, if you agree, the order is made. Some taxi services accept credit/debit cards for peyment, ask the operator about that option if you need it. The cost of a trip is fixed, you can leave a tip as a change from the .
The taxi will arrive by the arranged time, when it comes to the place the taxi service will send the message to your specified phone number or the driver will call you to name the car number and the color of it. Not all the taxis have an identification mark of a taxi. Nevertheless, if all the information on a car number and a name of the driver coincides with the information specified to you, that is your car, you can go.
Unfortunately, not all the companies have English-speaking operators and the English website; I have made a small list an English-speaking companies where you can order a taxi online:
Angel Taxi, (+7) 812 777 20 10,
Taxi 068, (+7) 812 068, (+7) 812 324 77 77,
New Yellow Taxi, (+7) 812 600 88 88,
Advice – do not use the services of the private cars – at a minimum you can overpay for the ride, at maximum it may be dangerous.