Phenibut is simply GABA that can cross the BBB easily. The effects are definitely comparable to xanax if not stronger. Xanax intensifies the effect of GABA on your brain. It all depends on the dose and how you react to it. As far as euphoria, a lot of people say it's the closest thing to ecstasy you can get. It is often compared to GHB as well. Chemically they are very close and from personal experience I can tell you it's the closest you're going to get. When dosed right I get an extreme sense of well being, like nothing in the world could bring me down. The most minor things can make you so happy etc. All of this while feeling like you have a 3-4 beer buzz. You lose a lot of inhibition. I feel like I could go up to anyone and just start up a conversation with them. I could go on. Seems like a lot of people don't do well at higher doses. I think I'm a little different because I've been on Klonopin for years which also works on GABA-B. I have quite the garden of receptors in my brain waiting. I remember when bulk nutrition sold it. The review section was full of "How in the **** is this stuff legal?" type comments. There were some going as far as saying "this is what I picture heroin feeling like".
If you want to use it recreationally, start low and work your way up to a dose you like. Everyone responds different. I usually drink coffee while using it to counter any drowsiness. I don't think I ever got the horrible hangovers etc. because I was on it pretty much all the time. The tolerance can make it an expensive habit.
I think it should be used more with recovering alcoholics. It mimics a lot of the effects of alcohol and helped me to get off the bottle.