Yes, I understand. I was just ruminating on the fig-leaf prudery of the shifted meaning. Now on to the etymology. Greek phallos is related to Latin follis 'leather bag, punching bag, bellows', English ballocks (from OE bealloc 'scrotum'), and Irish balc (unglossed, Hibernicus?). Greek ithus 'straight' has one Sanskrit cognate: sAdhati 'to come to the goal'.