Hi! i buy a IPhone on Ebay and I send the package by USPS to Florida and USPS lost my package with my phone I got the Imei and the serial how can you help found my phone back

Sort to hear your phone is lost with the carrier you used to ship it. If the phone was set up and Find My turned on you can follow Find your lost iPhone or iPad with Find My - Apple Support

If not, there is nothing Apple can do to help further. You’ll need to speak with the carrier you used.

As the device isn't set up with your account, you cannot find it. You'll have to file a claim with USPS.

iPhones are not tracked by IMEI or Serial Number, so we are unfortunately not going to be able to help on this one.

Once you have set up a phone with your Apple ID and Password, the phone can be tracked by using the Find My application.

Ask the seller for a tracking number and check with USPS.