Chances are you will never see your phone again. Most stolen phones are never recovered.
But if you had Find My turned on, you can mark the phone as Lost, making the phone much less useful to the thief or to anyone who the thief might try to sell the phone to. Hopefully your phone was locked with a passcode which the thief did not know and could not easily guess; that will be the first line of defense to keep the thief from getting at the data on the phone, until the phone learns that it is Lost, and locks itself up more completely.
You may also want to ask your carrier to blacklist the phone, so that the stolen phone will never get cellular phone, text, or data service from any carrier who honors the blacklist. (This may interfere with the phone's ability to learn that it is Lost or that you have requested a remote Erase, and with the phone's ability to report its own location.)