Most sources tend to point to him ruling the universe, though likely not it's entirety seeing as how the worlds of Babidi's minions and his actions in general went unnoticed. This would fit with the amount of sentient worlds being reduced to 28 by the time of Super, though him ruling only a galaxy would make more sense when considering the Freeza Force couldn't even find one Northern Quadrant world such as New Namek. Factoring GT, it's far less likely Freeza ruled more than one galaxy when so many worlds such as Imegga and M2 went completely under his radar and the corners of the Universe held warriors powerful enough to oneshot him, even jabronis like Zunama.
Most likely, he only had control of one galaxy, though maybe Cold's control extended far further. Perhaps he simply spread his empire out across too many galaxies to have complete governance over the Milky Way or scour the far reaches of space.