Applecare

Go here and find out:

Buy an AppleCare plan - Apple Support

AppleCare Products - iPhone - Apple

There is no such thing as a “new” iPhone sold on eBay. Apple and authorized retailers do not sell iPhones on eBay.

Any iPhone you can buy there is, by definition, “used”, even if the box has never been opened.

AppleCare+ can only be added within 60 days of when the device was originally sold by Apple or an authorized retailer.

Whether you will be able to add it will depend on how long ago the phone was sold at retail and in what country it was originally sold.

Call Apple Support at 1-800-APLCARE.

Or -> If you still need help buying an AppleCare plan, contact Apple Support.