I've only mixed phenibut with alcohol once, and won't do so again. I have no tolerance to alcohol whatsoever, as I dislike its effects greatly, but on that occasion I had less than a single beer with a regular dose (around 1.5 grams for me) of phenibut, and I was shoshed (physically, not mentally). I was so tired and uincoordinated that I just had to fall asleep, and I felt dizzy and shitty the next morning.
For me, phenibut took some getting used to. The first few times I took it, it made me quite uncoordinated and dizzy. After that, a dose of 1.5 grams or a little more or less began to provide me with a very smooth and natural, almost transparent euphoria, in the sense that it felt like I was just having an extremely good day, the kind of day where you wake up to the sun shining and 70 degree weather and the smell of spring after a long winter and you just feel overflowing with joy. It makes me want to move a lot because it feels good to do so, and in that sense gives me a lot of energy, but at the same time it makes it easier to get randomly tired when I'm sitting down and not doing much. It totally erases any anxiety I might have. It has pretty significant muscle relaxant properties but mentally it leaves my mind sharp, although in social settings my inhibitions are definitely lowered. In that way, I find it very good for sex, although it doesn't seem to actually physically enhance anything there.
I find that taking my whole dose at once is the best way to do it. It results in the clearest effect with no side effects. If I take my doses spread out, or even worse, if I take an additional dose after the first, it makes my muscles start to ache in the same way that they do when I've drank some alcohol... it just generally makes my body feel tense and unpleasant. Phenibut lasts all day... I've never taken it after 2pm. It takes 2-3 hours to really be noticeable, for me. It's not really a drug-like effect so much as an enhancement effect on the state of mind you're in. As such, it provides absolutely no rush or strong buzz of any kind. There's bo noticeable drop-off or comedown, either. You just eventually are not affected anymore. I really do love the stuff, but I find that if I take it too often it will start to be ineffective almost no matter how much I take (actually some of the effects always happen but the euphoria does not). I give it at least a day between doses but generally several days or more.
Personally, I enjoy it more than any other GABAergic drug I've tried (although I've not tried GHB). I don't get any euphoria or recreational effects from benzos (I find them boring, zombifying, and entirely pointless unless you're battling anxiety or something), and I dislike alclhol greatly, but phenibut is very nice. But again, if you're looking for some new drug of abuse, don't expect phenibut to do it for you. It's not like that.
) Ketamine. They seemed to not interact at all. But I have rather high GABA tolerance and Phenibut seems to do nothing to me besides stop withdrawals (very efficiently, must I add). 
