The version of Sphinx who was defeated by Galactus was standard Sphinx with a single ka stone. At that level he was often referred to as "godlike" and certainly displayed powers beyond typical heralds. With 2 x ka stones his powers increased geometrically and he was showing vast magical powers of energy, time, and reality manipulation. In fact his powers seemed to threaten the fabric of reality.
With 2 x moonstones Zemo also displayed some impressive powers of energy and time/space manipulation. He defeated Grandmaster and shut down Genis' out of control powers.
Been a while since I read those stories and neither of them were around for long (especially the enhanced Sphinx) but they both had some pretty high end powers, though they didn't really get to show the limits of them.
Didn't Nova Prime shield himself from Sphinx with 2 Ka Stones? He sure was powerful but not Tyrant powerful. Nova Prime would be lucky to shield himself from a Tyrant fart bubble.
Well, guys like the FF and Quasar have shielded themselves from Galactus's attacks at times, that's not always an indicator of power limits. Sphinx seemed to have reality warping powers though. By the end of that story he was going to remake reality and change the laws of physics or something. I think Reed thought he was capable of destroying the universe or some such catastrophe.