Phantasmal Sphere is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flying At the beginning of your upkeep, put a +1/+1 counter on this creature, then sacrifice this creature unless you pay for each +1/+1 counter on it. When this creature 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 this creature.