Uber scam

My friend booked an Uber cab and it wasn't moving. He sent a text asking for Phone Number in the app itself. She didn't give any number at first but then he started to spam the chat asking for phone number and she thought maybe he couldn't call her for some reason via Uber that's why asking for number. So she sent her number to the driver expecting a call from him. There was a warning about not sharing phone number in the chat which was ignored. Just after few secs of sharing the phone number, the ride was started without even her being in the car. She wondered how can an Uber start a ride without a pin as she needs to share the pin and she could see the car nowhere. When trying to cancel the ride, it showed that it would charge extra money and so she decided not to cancel it yet and tried to check other options to complain to Uber. The cab driver ended the trip and money was deducted automatically as she had online payment set up. Although she was successful to get the refund for the same on reporting it in Uber, I wanted to know how can someone start ride without the pin being shared? What did he do with the phone number ?