When you pay for an hour of editing from me, you are getting an actual hour of editing, during which time I am fully engaged with your text or fully engaged with you about your text.
I don't use a clock to judge my billable time but rather a stopwatch, which I start and stop often as I take breaks. So you don't pay for my coffee break time, my downtime checking email, or my time spent arranging my pencils in order of preference. I trust you to pay me, and I assume you want to be able to trust me not to waste your money.
I do not generally charge for the time used to make phone calls or emails back and forth, unless they are directly related to the editing of the text and are somewhat complex. I also do not charge for time used scanning in hard copies of edited work to be sent to you as a PDF. It's not your fault my scanner is slow.