I think there are general characteristics that are true for most people. I would be very hesitant to say “all people” for anything really. There’s always exceptions for the rule and humans are so complicated it’s nearly impossible to say that everyone does things the exact same way. For instance, there are people who have atypical stuttering patterns alongside the typical block/prolongation/repetition speech. My personal experience, the answer is no it’s not the same for everyone because it’s not for me. I don’t become more fluent when off the phone. I also stutter sometimes when talking to myself alone or on voice recordings. Now as to if that’s a general concept across a majority of stutterers, I don’t know because I haven’t heard of that being studied or evaluated before. It may or may not be. Personally I stutter significantly less in high stress situations than I do in relax situations. I have friends that are similar and some that are different.