What date did eBay give you for delivery?
That is the earliest date you can open an eBay dispute for Item Not Received (INR).
Go to your My eBay (Top Right of this page)
Go to-> Purchases - the cell phone should be there.
Go to-> More Actions- it's a dropdown menu
Go to-> Contact Seller and ask for the date sent and service used. These are not important but you also ask for the Tracking Number.
Use the tracking number to find out if your phone has been sent.
If it has, relax - the seller was stupid not to mark your purchase sent and give eBay that number because it affects his seller metrics, but that is not your problem.
If it has not, you have a different set of actions to take. Come back here and let us know.