Just thought I would update this with my experience since it seems not many have tried this combo. I went ahead and tried it after researching and felt that at small doses it should be relatively safe. I used 500mg of phenibut and 3g of kratom at the same time. Effects were very pleasant, I felt very relaxed and anxiety free. My hope was that the music would be more enhanced as phenibut tends to make it sound more vibrant. This effect was there however I feel the kratom took away from it a bit. I also was very social which is to be expected when using either substance. I had phenomenal sleep and did have some trouble waking up. There was a definite grogginess. I have noticed a bit of a fog today (next day) but my stress has been kept at bay.
Would I do this combo again? Maybe, but probably only for a special occasion. While I enjoyed the combo, I can definitely tell how a person could get addicted to this combo. The after effects also seemed to be more pronounced than if I had used kratom or phenibut solo, which to me isn't worth it. My consensus is that using either solo is best for me as each tends to have similar but slightly different effects.