Yes, Uber is mobile app only. That's the whole point... a mobile-based cashless transaction.
You could install the app onto a tablet, but you need a mobile phone number.
Def some cities are better than others in terms of coverage and ability. SF (being their home city) is usually great, won't wait longer than 5 minutes for a car.
Had a 7 minute wait in Boston today in the suburbs.
Do you fear taxis as much as Uber?
Hope that helps.