This should point you in the right direction.
I did similar thing to that BUT on opensource firmware from here: [OpenWrt Wiki] GL.iNet GL-MT300N V2
Also, my setup is based on E3372H-153 BUT on custom firmware from 4PDA.ru so there might be some differences.
As far as I can remember, E3372 has 2 modes of operation and somehow it was important in my setup, but I don’t really remember more details.
I advise you to first try to setup your phone as tether, this should help you understand what needs to be done.