How to direct internet connection to iPhone USB and not Wifi
There are at least two ways! First make sure that the iPhone is above WiFi in the network service order; that makes it the default for all traffic.  Then you can either:


Use SSH's -b &lt;ip&gt; flag to bind SSH to your desired IP. So if your WiFi IP is 
111.111.111.111, ssh as per usual with ssh -b 111.111.111.111.
Add a static route to your remote host routing through the desired IP. If your desired IP to connect from is 111.111.111.111 and your remote host is 222.222.222.222: $ sudo route add 222.222.222.222 111.111.111.111. then SSH normally. When you're done, tear down the route with $ sudo route delete 222.222.222.222 111.111.111.111.