Your phone is probably just not putting out enough power to drive the Fulla 2 directly. Few phones can. I have a (so far very short) list of phones that can on the first post of this thread.
Try first connecting a USB charger or battery pack to the Fulla 2's 'power-only' USB port, and then connect your phone to the other USB port and the Fulla 2 should start working as intended.
If it still isn't working, you may have gotten one of the early faulty units, and I would contact Schiit directly to find out for sure.
Latest model for the one plus one?