I'm by no means a financial advisor, but I believe whichever brokerage firm sold you (or me) "phantom shares" will still need to make good (cover) on those shares regardless of their origins if an RS, special dividend or other event that mandated accountability of the real shares occurred. Last thing they want is to get a bad reputation of stealing from its customers.

I came across an interesting comment letter on the SEC's website regarding naked short selling.

SEC Comment Letter