A VEI 3 or 4 seems most likely. A VEI 6 is possible, or even a VEI 7. That would be very bad for Manilla and cause global cooling.
Mount St Helens was a VEI 5 or there abouts. A VEI 6 is ten times largerthan the prior. So if St Helens is one foot, then the VEI 6 is ten feet. A VEI seven is 100 feet. A VEI 8 is 1000 feet. Just to put it in perspective.
Then comes the duration. Two days? Four? One week? Two weeks?
Yellowstone was the second largest known behind Toba. The third or fourth? The Long Valley eruption..And that one has the magma ABOVE the valley floor at this time in the mountains around it.