What else do I need to do after changing my Apple ID password for a lost iPhone?

If you’re assuming that your phone is forever lost …

If your iPhone or iPad was stolen - Apple Support

Whatever you do, be extremely careful if you receive a message from "Apple" or "Apple Support" or "Service" etc that indicates that your iPhone has been found and you just need to log on to remove the device from your list of devices using your Apple Account ID.

Anything like this is a SCAM that is trying to trick you into removing the Activation Lock protection from the phone so the bad guys can get into your phone and do just about anything they want.

You need to ignore any messages like this because Apple does not get involved with lost or stolen phones.....so you know that Apple could not have sent the message.