The only time I had phenibut I was determined to get wasted and took it with temazepam and lashings of alcohol. It resulted in what I imagine to be a GABA overload; I had vertigo, felt sick (I think I did actually vomit), disorientated, uncoordinated and generally awful. A little like when you have had too much to drunk, or too much GBL/GHB.. I would not recommend this to anyone!
I know we always bang on about combining CNS depressants, but there is a good reason for that - they can and do kill people. In this case I suspect it wouldn't be fatal, just unpleasant, but combining benzos and alcohol on their own often leads to disaster, let alone adding in phenibut..
You haven't actually mentioned alcohol, and it sounds like phenibut gives you the same effects alcohol does (eg more talkative and at ease in social situations) so I would pick one of the two. And still go steady, this forum is full of stories of mishaps involving the combining of alcohol and benzos, and the resulting impaired judgement and amnesia..