Barbiturates are more dangerous than benzodiazepines, but phenobarbital isn't really one that's more dangerous. The dangerous ones are Pentobarbital, Secobarbital, and Amobarbital (other than the Ultra-Short Acting ones that are used for surgery, like Thiopental (Sodium Pentothal), but you're not gonna have access to those unless you're an anesthesiologist).
Butalbital would be more dangerous to combine opioids with than Phenobarbital, and it's combined with 30mg of codeine in Fioricet #3 w/ Codeine which would be equivalent to half a 10mg Norco.