If she got calls like "I'll pay someone $1000 for a ride to the airport right now", that might justify Uber hiring people to answer phones. But she doesn't, she gets calls from angry harassed customers and people who don't know they can't schedule future rides. Guess what, Uber doesn't want or need to hear from these people. They've optimized to reach people who make them profit, not who are a time and money sink. Adding a phone number is only down-side for them and they clearly know it.