Find my is on but when I look for location it said online but no location found

In order for your lost iPhone to "report in," it has to be connected to the Internet. That could either be by a Wi-Fi or cellular data connection. Until it does, at best, you would see a "last known location" in the Find My app in iCloud.com.

Potentially, if you enabled "Find My Network" on this phone, other Apple devices could locate it and report its location.