Xcode 9 Wireless debugging not working

Make sure System Preferences->Internet Sharing is enabled using USB ports:

I had the same issue, but it was intermittent - i.e. sometimes the globe would not appear next to the phone name in Xcode Devices and Simulators window and when the phone was disconnected from the lighting cable, I could not debug to it from Xcode. My fix was much simpler, though - I just turned WiFi on and off both on the Mac and on the phone. After the devices reconnected to the network wireless debugging was available again. This seems to be an issue with the network communication (regardless whether the device can be pinged or not).