Ebay will accept phishing reports via email at spoof@ebay.com

Forward the original mail with full headers. Most email apps suppress most of the header info since users normally don't care about anything other than where it came from (usually wrong for these things) and the subject line.

The good info that helps locate (sometimes) the sender is hidden unless you show full headers. Different email apps use different commands for showing the full headers so poke around a bit or post which email app you're using and somebody with access to that app can give the exact command/menu/etc.

I've sent lots of phishing reports to ebay and paypal. They're usually pretty quick about verifying if it's a scam and they have an auto reply setup with detailed info on generally avoiding the problem.