How long has your dog
been taking the phenobarbital...? If the pheno is a new med for your dog
, maybe the dosage needs to be adjusted.
As far as the rescue remedy goes....if you think it might be doing some harm, or possibly interacting with the pheno...then by all means stop giving it.
If you want to try something natural to help calm him, just try Lavender essential oil...put a drop or two on his collar...or rub a drop or two on his chest.