If you back your PP account with a credit card, you can go to the 1-800 number on the card, phone and ask the customer service clerk about a chargeback.
But cards have deadlines too.
Most warranties are from the manufacturer, not the retailer, and you may have some information on the paperwork that came with the phone about that. But if it is a counterfeit phone, that's gonna be a dead end. Try it anyway.
How long did the phone last before breaking down?
If either you or the seller left feedback, you can leave a Response to that FB indefinitely. Although this does not affect his ratings, Responses do stand out on a page.
Like the best FB, the best Responses are calm and factual. 'Broke after 6 months, told phone is counterfeit by shop.' for example.
You could also Report the seller to eBay for selling counterfeits, which is illegal.