Get deleted messages

If you were using iCloud messages, there is no way to recover them. If you were not, if you have a backup of the iPhone made when the message was on the device, and you have not created a backup of the device since you deleted the message, you can restore the iPhone to that backup and the message should reappear. If you do not have a backup, or have a backup that was made after the message was deleted, you are out of luck.