Find My Iphone

It probably has been erased and now is activation locked. Do not remove it from your device list. See If your iPhone, iPad, or iPod touch is lost or stolen  https://support.apple.com/en-us/HT201472

From the document: Erase your device. To prevent anyone else from accessing the data on your missing device, you can erase it remotely. When you erase your device, all of your information (including credit, debit, or prepaid cards for Apple Pay) is deleted from the device, and you won't be able to find it using the Find My app or Find iPhone on iCloud.com. After you erase a device, you can't track it. If you remove the device from your account after you erase it, Activation Lock will be turned off. This allows another person to turn on and use your device."