I'm not sure why you can't find scientific confirmation of the pharmachologic effects. The wikipedia link above provides some reasonable references that are easily accessible (at least here in the US, maybe in Poland it's different). There are something like 300 scientific publications (although most in Russian) evaluating its effects.
If it's personal experience you are looking for, I can tell you that I've been using it for the last month and can personally attest to it's beneficial effects for SA. I'm using Primaforce brand powder. Because of horror stories I'd read on other sites about how addictive it is and how bad the withdrawl could be, I started with 300 mg doses taken a few days apart. It's anxiolytic effect even at this dose was dramatic and lasted an entire work day, and I experienced no hangover after it washed out of my system.
I've since increased my dosage to up to 1g a day. I'm still being careful to take a break from it every second or third day, but I haven't had any of the rebound effects coming off of it that I've heard described elsewhere. My SA comes back after the phenibut's effect wears off, but it's no worse than it was before I started taking it.
As someone mentioned above, and as with any drug (and this is clearly a drug--not a "supplement," whatever that is), YOUR RESULTS MAY VARY. I certainly suggest caution to anybody who tries this. It's chemical properties are close enough to benzo's that you don't want to mix it with alcohol or anything else that messes around with your gabanergic system, and you probably don't want to be depending on it on a daily basis. It's had amazing effects for me, but if that changes, I'll be the first to come back here and tell you how much of nightmare drug it is.