I have published in ASPLOS and HotOS with a bachelor's in computer science, though some of my co-authors either had or were pursuing PhDs. Publishing and PhDs are correlated, but not necessarily causally related. I.e., the same impulse that causes people to publish causes them to pursue research careers.

There's no shaggy-dog story of how we broke into the big leagues. We submitted the way everybody else does, and the anonymous peer review process never demanded our grad school union card. We had the benefit of amazing, experienced readers giving us unsparing feedback long before submitting, and had the good luck of having built an interesting system with some weird properties. Having something to say that your peers might find interesting is the hard part, not collecting qualifications.