Honestly, you never know these days. There have been a lot of horror stories later, especially as eBay has been shifting more and more to buyer rights and not seller rights.
He could claim you sent him a box with a bunch of rocks in it, take pictures of some rocks in your iPhone box, submit it as proof, etc.
I'm not saying this will happen, but when buyers pull crap like this, eBay frequently sides with them. I would go to a FedEx or UPS ship center and pack the phone in front of them, showing that it's sealed (or opened if you have done that). Have the person be a witness that you sent a legitimate package just in case. It really is worth the extra effort just to be safe.