Use an iPhone 6 as a monitor for a Raspberry Pi via USB
Congratulations on the Pi - they’re lots of fun.
iPhone hardware doesn’t have a video in through the lightning connector, so you’d need a different option even if the Pi had drivers to send data out over USB.
You’ll want a driver board and touch or no-touch display like these for the most economical solution if you don’t use HDMI or more traditional video out.

https://www.raspberrypi.org/products/raspberry-pi-touch-display/
https://www.adafruit.com/product/2718
https://www.adafruit.com/product/1933