Greek phallos is related to Latin follis 'leather bag, punching bag, bellows', English ballocks (from OE bealloc 'scrotum'), and Irish balc (unglossed, Hibernicus?).
The word "ballocks" or "bollocks" I had always assumed to be formed from "ball", but your source suggests it's related to words for bags and bellows.

The Irish word you list is probably modern Irish "bolg" meaning "belly". "Belly" itself looks like a cognate, and if so the semantic connection to a leather bag is by no means unreasonable.