Thank you for the setup. All guides arround the internet are basically the same. The thing is that windows phone adds the devicename to the username (for whatever reason). For the rest it is a standard IKeV2/IPSec setup. And works fine on a Raspberry PI. I prefer to use the installation through AUR. Although it means things will need to be compiled (and that takes quite a while).
I found some issues using your guide (and many others). One major thing is that the name and location of the sysctl.conf is changed (which was the reason no data came through) in Arch Linux (see archlinux sysctl documentation note on top of the document, I cannot post links here yet). The other (probably because I am not used to working with Linux) is that the iptables will not be permanent (after reboot) if you do not save and enable the service (Again check the Archlinux iptables configuration documentation, this explains how to make it permanent). I post this here so you can add it to your guide..