Can I convert ONE 3 phase connection power supply to become TWO 3 phase connections?
Assuming you mean receptacle, yes you can split a split a three phase branch circuit into multiple receptacles the same way it is done for regular 120V circuits. It's rare though as most three phase machinery draws a lot of power which warrants dedicated circuits. But, if you have a small shop and you only use one machine at a time, then it's fine.

My grandfather had a mini shop inside my fathers shop and he had a single 20A 208V circuit that ran to three twist lock outlets. He had a mill, lathe and surface grinder. All of which could easily share a single circuit because he never ran more than one at a time.