That looks like a fake web site for Apple. Probably the thieves phishing for your log-in information so they can remove activation lock and make the phone usable to them.
Log into Find My using iCloud or use the Find My app on another person's device.
Read how to 'Use the Find My app to locate a lost or stolen device'. Click here --> https://support.apple.com/HT210515#locate
A person can use the Find My app on a device owned by someone in their Family Sharing group. Alternatively, anybody can sign into https://www.icloud.com/find to locate their device using a browser.
Click on this link for general information about what to do "If your iPhone, iPad, or iPod touch is lost or stolen" --> https://support.apple.com/HT201472