How can I get a copy of my iPhone receipt?

If you bought the iPhone from Apple directly, and linked your Apple ID to that purchase, then you can get receipts through your personal Store portal: the shopping bag icon in the upper right corner on any apple.com web page.

If not an online purchase, then contact the Store where you bought it. They should be able to tell what they need to reproduce a receipt.

If you paid in store you may not be able to get another copy after so much time. You can contact the store but they may not be able to help you. Reach out to the store