Taper slowly is all I have to offer really. I got horrendous w/d from phenibut - easily some of the worst I've ever had from anything - and actually ended up using GBL to taper with. I must say that worked a treat and was completely painless but I've never had problems tapering GBL anyway which probably helped a lot. I certainly wouldn't recommend stopping dead cos it's pretty brutal on the GABA-bashing is phenibut. Took a few days for that side to really kick in but it was just plain nasty - jittery, anxious, feeling like I was about to faint all the time. I really couldn't deal with it myself so went with the devil I know.
I'll keep this thread separate for you if you like but you may get more responses in the main phenibut thread as many people have had issues when it comes to stopping the stuff. Sneaky fukker is phenibut. Give me a shout if you'd like it merged and good luck with getting off the stuff