Dre is about to sing his verse; he is being called to the mic. Creeping is also driving and a phantom is a type of rolls-royce, so his flow or style of rap is smooth like a ride in an quality vehicle. "approach in a smooth, ghostlike manner"
He is saying that when one of his "bitches" makes a business transaction (sexual intercourse in exchange for money) with her customer, that he will be taking his percentage. Much like how the Federal Government does with legal business transactions.