RaspberryPi as a "bridge" between router and Hotspot

I'm not sure if this is the correct spot to post this. But I've search for what I'm trying to do and not finding anything.
I want to connect my existing router via LAN/WAN to a Raspberry Pi. The Pi will also have a USB tether to an android phone, then the Android phone will connect via WiFi to an iPhone WiFi hot-spot.
Why do I need to do this? The iPhone doesn't auto start the USB tether without user action. I need to be able to have it auto connect after power outage or reboot.

router LAN/WAN > eth0 Android USB tether > iPhone hot-spot

So what I've done is downloaded the USB packages and have the USB tether device in interface following the tutorial.

What I'm not sure on doing now is how to setup the USB0 and eth0 to just pass all the info from one to the other so the router just basically is connected to the iPhone's hot-spot.

FYI, the router (Archer C7 V1) is currently using the iPhone USB tether.
I can't install OpenWRT on the router.
Because every time it reboots I've got to trust the device on the iPhone. So this is why I'm using the Raspberry Pi with OpenWRT to be the bridge between the two devices.

Any assistance would be appreciated, even if it is just a link to the correct tutorial.