The American Express New Accounts Team will dial out from a common phone number 1-+1 866-379-3643 when something unusual about an application for a new card has been submitted. As an example, if fraud prevention and identification believes that someone is using another's identity to submit an application, the department may reach out to confirm, you are the person who has submitted the application. People are often surprised by the call, and may believe it to be phishing and not realize the reason they're receiving the call is because there was something suspicious about the application. See more about types of fraud at: https://www.americanexpress.com/us/security-center/types-of-fraud/