Lost phone

If you bought AppleCare+ with Theft & Loss when you got the phone, or bought insurance through your carrier, then there is coverage. If you didn’t do either see if your homeowners/renters insurance covers it, or if you have a premium credit card that would cover loss.

Meanwhile, see→If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

If you have already lost the phone without an insurance policy unfortunately there's nothing you can do, if you get a new phone be sure to take out an insurance policy.