vpn tunnel using iphone as router

I have made up a personal vpn server, since I switch on this vpn from my phone I suppose that all devices who connect to my phone are using vpn tunnel for any communication. came out that the communications from my Mac connected tho iPhone uses the mobile provider network not the iPhone tunnel. actually I have to switch on the vpn on every device.. how's that? to be sure I only check my ip, and have different ip from my phone who is sitting on vpn. Can anyone explain how to fix it? idk how come the phone provider can see and trace my Mac behind the iPhone.