iOS hotspot + VPN behavior
As of iOS 11.2.6, if using the Personal Hotspot feature, any devices connected to the hotspot will show whatever the phone's public address is (eg from Verizon Wireless).

Interestingly, the phone will show that it is connected to the VPN.

If you run a web-based IP check, the phone will display the VPN's address (as expected), but connected devices will have the non-VPN address.

For example, your iPhone might display 44.33.22.11, because it's where the VPN is, but the laptop may show 77.55.33.11 because that's what the phone has for an underlying IP.

I don't know why this is - but it is what it is.