LOST IPHONE

The only steps you can perform are listed here:--> If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support, and/or here:--> Use the Find My app to locate a missing device or item - Apple Support

Regards

Giulio

There's nothing you can do. You can change the passwords for your online accounts, but if you had a strong passcode set on the phone, the data on the device is encrypted.