Anyone ever did a study on the meaningless gestures we do when speaking to people over the phone? Meaningless because the person at the other end of the line has no clue what you’re doing at your end, and meaningless because the gestures generally have no correlation whatsoever with the object, action, state of mind, etc. you subconsciously want to describe or illustrate.
I think the need to accentuate what we are saying by using hand gestures is such a big part of language itself, that it simply comes naturally while speaking, whether face-to-face, or on the phone. I’m pretty sure Morris covered this very topic somewhere in ‘The Human Animal’.