They will send an automated email to your Apple ID email address saying the phone has been put in Lost mode. If you don’t see that check your spam or junk email folder.
You can also go to https://icloud.com/find to view the lost mode status.
If you erase the phone and you later recover it you would have to restore a backup to the phone (or its replacement). And once you erase it you can no longer track its location, but it will still be “attached” to your Apple ID account.
Beware of a common phishing scam: You may get a text or email from “Apple” or “Apple Security” (or sometimes “Police”) saying your phone has been found and to click on a link to see its location. This is NEVER from Apple or from law enforcement; it is from the thief or fence to steal your Apple ID and identity. Delete any such message without responding to it. Apple never gets involved in lost or stolen devices→Avoid phishing emails, fake ‘virus‘ alerts, phony support calls, and other scams