The basic eBay Buyer Protection policy is the Money Back Guarantee.
Which as you have learned means if there is a problem you get your money back.
Once you got your money back the transaction was over. The phone now belongs to the seller, who paid you for it by refunding even the shipping cost both ways, which is a loss for him.
bought an unlocked refurbished phone from a seller and they never had it in stock. I heard Ebay sellers can do this.
No.
We are not supposed to sell anything that we do not have in stock.*
Whether or not you opened a formal eBay Dispute, the seller did the right thing.
He sent you return shipping.
He refunded you promptly.
The exchange rate is always a gamble. It varies from day to day. You lost money on the exchange but would you be complaining if you had made money on it?
*This is complicated with pre-sales of new items (but your purchase was of an existing item) and dropshipping (but the reseller has a contract with the supplier).