How do I select USB as the input source for internet on an iPhone when Reverse Tethering?

I have Sharing activated on my MacBook Pro. If I specify Ethernet as the input source and either WiFi or Bluetooth as the output, I can reverse tether to my iPhone 7 (running iOS 13.1.2). In other words the laptop is feeding internet to the phone.

However if I instead choose “iPhone USB” as the output on the laptop and hardwire to the phone with a USB-to-Lightning cable, I cannot access the internet on my iPhone. The problem is that while you can select WiFi or Bluetooth (or cellular data) as the input source in the iPhone Settings, there does not seem to be a way to choose USB.

Does anyone know how to do this?