Plug a guitar amp into iPhone

I need help with getting GarageBand to recognize my guitar input. The way I have it set up is my guitar into my amp, then the headphone jack on my amp is being wired into a 3.5mm USB hub that is connected into my iPhone. When I scroll around my phone, I can hear the guitar being played through the amp no problem, however when I use the guitar amps on GarageBand and turn on monitoring, all I hear is the pickups from the phones mic.

Anyone know how I can re-work this??? Trying to get the guitar to go through koala as well!