The short answer is yes.
Long answer: Ideally, I like the first few sessions to be in-person. It helps me build a better rapport, which I think is very important. After the intro stage, online tutoring is just as effective as in-person.
For the best experience, it’s necessary to have the right tools. I haven’t experimented with everything but so far I recommend an iPad, a stylus, and decent WiFi. The new iPads with an Apple pencil are perfect. Headphones also help with potential background noise.
As we cover more work there is a point where most of the tutoring is as “simple” as discussing problems. I just need to know which problem they are having trouble with and we can just discuss it over the phone. I don’t need to see them work it out, and they don’t need to see me work it out. They just need pointers.
So yes, after a certain point phone call tutoring can be just as effective as in-person tutoring. So even if a student is in the mountains, as long as they have a signal, they have no excuse to fall behind with the tutoring.