I lost my I phone

If you had a passcode on your phone nothing is accessible on it.

For added security, if Find My was enabled on the phone before it was lost you can remotely erase it. You will find details about lost iPhones and iPads in this link→If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Log in to https://icloud.com/find, click on your device and erase it. Do not remove it from your account. As long as it is still connected to your account no one will ever be able to use that phone.