lost i phone
My granddaughter lost her phone need her device put i lock mode
Question marked as
See this link for what to do if your iPhone is lost or stolen. It presumes your granddaughter had turned on Find My and it's powered on and connected to a network. If it Find My was not enabled you can't block it remotely. You should contact the cellular provider the phone was with to have them Blacklist the phone.
Click here for more details --> If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support