Did you mark the phone as lost and then leave a contact number? If not, then likely it is the thieves who have found the number and are now phishing for more information. There is a good chance it is a scam, particularly if there is a link to an "Apple" web site. Apart from supplying the Find My app, Apple does not get involved with lost or stolen devices.
Scams (e-mail, text messages, and phone calls) are getting very good at closely imitating true Apple communications. Always be cautious. These support articles have some guidelines:
About identifying legitimate emails from the App Store and iTunes Store --> Identify legitimate emails from the App Store or iTunes Store - Apple Support
Recognize and avoid phishing messages, phony support calls, and other scams - Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support
Avoid scams when you use Apple Cash --> Avoid scams when you use Apple Cash - Apple Support
Apple 'How to identify, avoid, and report phishing' video--> https://youtu.be/SR3Z3fXXjfw
This document has a list of things to do if your iPhone, iPad, or iPod touch is lost or stolen. --> If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support