Phillip II controlled roughly half of modern Greece size-wise, so 25K sq.m. At best, if we include his later (unstable) expansion territories, like the Peloponnese, he'd be at something like 35K sq.m. Not sure where 0.3M sq. miles comes from (that would be 8 to 12 times the area).

For Alexander the numbers I find are about "two million square miles".

2M / 25K gives 1/80. Round it up to 1/100 and let's call it a day.

1000x was an off the cuff number, with the point being the huge increase in the size of the kingdom Alexander inherited - not the specific multiplier.