Several things I'd like to mention.
Firstly, an error in math in my previous post. I mistakenly multiplied each phl16 launcher by 10, instead of by 8. Of course, phl16 carries 8 370mm missiles, not 10. So in the event there are (just) 48 launchers, then the minimum missile count is not 480 but 384.
Secondly, I am not sure about 300mm missiles not being able to reach 200km.
370mm ones used in phl16 don't really have proper sources for their ranges. Yes, 220 km is sometimes mentioned by various blogs. But so is 350 km, with the 220 figure being written as miles. But none of that really means much without a proper source.
Now, we can't know the range of PLA's weapons but we do have circumstantial evidence suggesting the technology might be there even for 300mm missiles to reach 200 km. We know that the GMLRS-ER rounds, which are smaller than phl03 and phl16 300mm rounds, both in diameter and length, can reach 150 km. Those have more or less finished development and are scheduled to enter production this year.
We also have the Polonez system, used by Belarus. During their military parade, it was announced that their Polonez can reach 200 km. Their ztem company states in their catalogue Polonez has a 200 km reach, with Polonez-M having a 290 km reach.
And, as we know, Polonez is in reality based on Chinese A200/A300 300mm missiles.
This is a missile fired from Polonez
And this is one fired from PHL03
Now, those are clearly two different missiles, details wise. (For one, A200/300 seem to be two stage missiles) That being said, they're still very similar in length and practically identical in diameter. Meaning that it's not very far fetched to ask the question: could the same missile used in polonez be also available to phl03 and phl16? Especially the phl16, with its more modular approach, might be a plausible fit.
Of course, we don't really know. There are no sources out there to confirm it either way.
We do, however, know that PLA has 14 artillery brigades. Most of those feature 12 phl03 launchers (though there is one brigade with 18 and one with at least 14 launchers photographed)
IF phl03 does have the option to use A200 or A300 tech derived missile - and if PLA has at least one load worth of such missiles per launcher, then suddenly it would be quite plausible that PLA has at least 10 (brigades without phl16) times 12 (minimum launchers per brigade) times 12 (tubes per launcher) missiles, for a total of 1440. Plus the 480 from four phl16 brigades. Close to 2000 missiles, on a single load per launcher assumed.
Not sure if A200/A300 missiles come with fins folded out of their tubes. If so, then the compatibility with phl03 tubes might be even greater.