Here's how I've got it: assuming you have a DC-DC 12v-5v Step Down (of at least 5A) or two in parallel for two 5V 3A outputs, use one of those as power for the hub. I believe Fast Charge requires 3.1 VDC. Then, you'll need a USB break out and a Micro-USB breakout for good measure. ( https://smile.amazon.com/MakerHawk-Adapter-Converter-Interface-Breakout/dp/B07MBSTZYG/) Now you'll need to solder the USB breakout the following way: pins GND, D+, D- and ID (3 inner most ones) to the corresponding pins on the Micro-USB. Then wire the GND (again) and VCC (outermost ones) to a 5V 3A power step down. Then use a simple Micro-USB adapter cable to the Micro-USB connected to the Pi, and a simple Type C USB cable from the USB breakout to charge your phone.
This will basically connect your phone's data and ground pins to the Raspberry Pi (for Music/Android Auto/etc.) and will use a fresh larger power source for the USB's power pin. The ground is common, so you'll be sure to have the same voltage on both devices.
Here's a simple schematic to better understand: