How to cancel a usps shipment?

I accidentally sold my iPhone 6 to a scammer around the end of August because I thought he had payed me because I received an email from Paypal. Turns out the email was a fake and there was no payments made. I checked the tracking number today and found out that the package is "in-transit" and had a redelivery scheduled on September 3. What does this mean? Is there anyway I can get my phone or the money? Is there a way to cancel the shipment?

You know you received payment when the money is deposited in your bank account. That is how we work with eBay. Never assume the buyer has paid. You obviously failed to actually check your balance and took the Paypal email as a legit source. You have lost both the money and the phone. Hope you have learnt a valuable lesson.