If the seller had delivery confirmation on it and it showed up as delivered, you may be SOL. I have found that info related to delivery confirmation is slow to hit their website, especially if you print the label and pay for postage online. Most sellers don’t buy insurance on USPS items unless the buyer asks and pays for it. Some offer it as an option on the invoice. I opt for the insurance if I’m buying something expensive or fragile. I’ve sold thousands of parts of eBay w/USPS shipping and only one thing has been broken, and nothing has ever gone missing. Knock on wood. But it ruins my day when some $100 part goes missing and I have to deal with threatening emails, even though it always shows up eventually. Don’t go after the seller if the phone shows up as delivered, nothing they can do at this point. Good luck!