As said iPhone is a host only device plus the PS3 doesn't support natitive A2DP, which is the bluetooth streaming audio standard.
You could by a A2DP transmitter then pair to existing A2DP headphones or just get something like
Sony's own PS3 wireless headphones.
Those headphones are overall pretty well rated from what I've read.
I've actually wasted money and time on trying to get bluetooth audio out of my PS3 in the past. I bought a A2DP transmitter that you plug the PS3 audio output into, the problem was the range was horrible and from what I've read, that's the case with the available options out there.
I literally couldn't sit on my couch and get a strong enough signal from where the transmitter was maybe tops 10' away.
If you're looking into this for playing any multiplayer games you'll really want to get either the headset I linked or the one from Turtle Beach that cost a lot more as they both allow you to proper adjust the chat and game audio channels separately.
Otherwise you'll find, as I did, that the chat audio at times can be deafening when the game audio levels are proper or oddly enough at times or with some games the complete opposite where you cannot hear the people talking via chat over the game audio.
Having a way to set the audio levels for both chat and game audio is a with the PS3.
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