My understanding is that you can log into iCloud, on the Web, and cancel a pending Erase request. Don't log in or provide your credentials in response to, or using any link that you might find, in a message. For all you know, that message could be from criminals who would use fraudulently-obtained credentials for no good.
https://www.icloud.com/find/
If the phone hasn't learned of the Erase request yet, and it doesn't have an Internet connection (e.g., because it is turned off), you can cancel the request.
If the phone has learned of the request, there is no way to take the request back. Any data on that phone is gone. Your only hope would be that you had previously stored that data in places outside of the phone (iCloud backups, iCloud synchronization, etc.).