I could be wrong but as a great grand son to a left handed Great Grandmother, who had to quit school by the time she was in the third grade, because back then before the 1930's or even a bit later. It was looked at by being left handed as "mentally Backward". They would slap/beat her hand every time she tried to use her left hand.
So as a note and opinion, I doubt anything in the USA before 1930 would have been made for left handed people. Especially a phone. Kinda make sense too, because only people, in the beginning that had phones look at their standing in the community as something big and a lefty would be a bad mark on the family. Just a fyi