Phone 54 is a mission in Grand Theft Auto 1 level 6, Rasta Blasta, given to the Protagonist by Brother Marcus. It is available from the payphone in southeast Miramire.
Mission
The mission begins with Brother Marcus informing the protagonist of Babylon's plan to kill his mother in order to get to him. The player needs to steal a Taxi and go and pick her up from southwest Greek Heights. She will then need to be taken back to her house in east Vice Shores to complete the mission.
If it takes too long to pick her up, she will get another Taxi sent by Babylon, and it will explode as she gets in. Thus, the mission will fail. There is no exact time limit however: sometimes the mission is failed even if the player gets near her as soon as possible, avoiding all cars, having triggered the mission already possessing a Taxi, and sometimes even some minutes elapse before she is killed.
Reward
The player will be awarded 40,000 points and a +1 score multiplier for completing the mission.
Grand Theft Auto 1 PC Vice City Chapter 2 - Mission 14