There is no buyer. There is only a scammer trying to steal your iphone.
He is not interested in your identity or bank account, only your iphone.
The check is FAKE and will NOT clear. Do not attempt to cash it, shred it and cease emailing that scammer.
The next email will be from another of the scammer's fake names and free email addresses pretending to be the "secretary/assistant/accountant" and will demand you cash a large fake check sent on a stolen UPS/FedEx billing account number and send the money via Western Union or moneygram back to the scammer posing as the "shipping company". When your bank realizes the check is fake and it bounces, you get the real life job of paying back the bank for the bounced check fees and all the bank's money you sent to an overseas criminal.
Western Union and moneygram do not verify anything on the form the sender fills out, not the name, not the street address, not the country, not even the gender of the receiver, it all means absolutely nothing. The clerk will not bother to check ID and will simply hand off your cash to whomever walks in the door with the MTCN# and question/answer. Neither company will tell the sender who picked up the cash, at what store location or even in what country your money walked out the door. Neither company has any kind of refund policy, money sent is money gone forever.
When you refuse to send him your cash he will send increasingly nasty and rude emails trying to convince you to go through with his scam. The scammer could also create another fake name and email address like "FBI@ gmail.com", "police_person @hotmail.com" or "investigator @yahoo.com" and send emails telling you the job is legit and you must cash the fake check and send your money to the scammer or you will face legal action. Just ignore, delete and block those email addresses. Although, reading a scammer's attempt at impersonating a law enforcement officer can be extremely funny.
Now that you have responded to a scammer, you are on his 'potential sucker' list, he will try again to separate you from your cash. He will send you more emails from his other free email addresses using another of his fake names with all kinds of stories of being the perfect buyer, great jobs, lottery winnings, millions in the bank and desperate, lonely, sexy singles. He will sell your email address to all his scamming buddies who will also send you dozens of fake emails all with the exact same goal, you sending them your cash via Western Union or moneygram.
You could post up the email address and the emails themselves that the scammer is using, it will help make your post more googlable for other suspicious potential victims to find when looking for information.
Do you know how to check the header of a received email? If not, you could google for information. Being able to read the header to determine the geographic location an email originated from will help you weed out the most obvious scams and scammers. Then delete and block that scammer. Don't bother to tell him that you know he is a scammer, it isn't worth your effort. He has one job in life, convincing victims to send him their hard-earned cash.
Whenever suspicious or just plain curious, google everything, website addresses, names used, companies mentioned, phone numbers given, all email addresses, even sentences from the emails as you might be unpleasantly surprised at what you find already posted online. You can also post/ask here and every scam-warner-anti-fraud-busting site you can find before taking a chance and losing money to a scammer.
If you google "fake check buyer scam", "fake Western Union buyer fraud" or something similar and you will find hundreds of posts of victims and near victims of this type of scam.