Hello emaches,
If the iPhone is not located in the Devices section of Find My, then ensure Find My iPhone is enabled under Settings > [name] > Find My > Find My iPhone. Check out that suggestion, and further troubleshooting in the article below:
If Find My is offline or not working - Apple Support
"I don't see my device in Find My
Make sure that you set up Find My on your device. You have to set up Find My before you can see your device in the Find My app or on iCloud.com/find.
. . .
If you have your device with you
- Check that you signed in to iCloud on your device: Tap Settings. If you see "Sign in to your [device]," tap it and enter your Apple ID and password.
- Make sure that you signed in to iCloud with the same Apple ID on all of your devices.
- Check that the device has a cellular or Wi-Fi network connection. If it does and you still can't see it in Find My, turn Airplane Mode on and off. Still not seeing it in Find My? Restart your device.
- Go to Settings > General > Date & Time. Check that Set Automatically is on.
The Find My network isn't supported in South Korea and might be unavailable in other regions due to local laws. In South Korea, you can play a sound on your device, mark it as lost, or erase it, but you won't be able to find your device on a map."
If the issue persists, reach out to Apple Support directly to help investigate the behavior. You can use the following link to reach out: Contact Apple Support
Kind regards.