My settings for phoenix 1.50 are:
-k phatk PLATFORM=0 DEVICE=0 VECTORS BFI_INT AGGRESSION=12 WORKSIZE=128 FASTLOOP=false

I just started my miner again and will see if it works now.

With regards to the work queue empty problem:
Try adding -q 3 before the -k switch in phoenix to have more than only one queue. You probably have to figure out which value is perfect for you .

Edit:
Seems to work perfectly now and I'm back to my usual 2%.