At the beginning of your upkeep, put a +1/+1 counter on Phantasmal Sphere, then sacrifice Phantasmal Sphere unless you pay
for each +1/+1 counter on it.
When Phantasmal Sphere leaves the battlefield, target opponent creates an X/X blue Orb creature token with flying, where X is the number of +1/+1 counters on Phantasmal Sphere.