Phoebe Smith's place wasn't close to the airport, and since she was a wheelchair user with disabilities, it even took some time to get back from the Imperial Hotel by taxi.
She hadn't been in London long and was disabled, so she didn't plan to buy a car, and usually relied on taxis for transportation.
Oscar Smith did have a car in the United Kingdom, but he had returned to his country, and his car wasn't parked at her apartment. So no matter how much of a rush she was in, she could only travel by hailing a taxi.
Sally, in fact, didn't want Phoebe to leave London because she was worried about her drug supply being compromised after Phoebe's departure. That's why her actions were sluggish and dragging.
"Sally, can't you hurry up!" Phoebe shouted impatiently, "I told you we're in a rush for time, yet you don't seem to be in any hurry at all. What do you mean by that?"