How do i find a serial number for a phone i no longer have

Hey there snr831,

Thanks for reaching out to Apple Support Communities. We understand you’d like to know how to find a serial number for an iPhone you no longer have. We’ll be happy to guide you on this.

If you no longer have the iPhone, the following info may help:

• “If you have your product's original packaging, you can check the barcode to find the serial number.
• You can also find your product's serial number on the original product receipt or invoice.”

Take a look at this article for more info:

Find the serial number of your Apple product 

Take care.