Phone missing

have you tried using your Apple Watch on the find my devices app?

There is only one chance to track your phone is when your phone is online.if you want to erase your iphone you can do it with find my phone website when phone come online then phone automatically erased.

The phone is "Offline" because the battery has run down or the phone does not have an Internet connection where it is currently located.

There is nothing that you can do about this except check Find My a few times each day to see if the status of the phone has changed.