Consider your dog poisoned, and get them to a vet asap!
First, induce vomiting. Either give them a dose of syrup of ipecac or stick your finger down their throat. The longer you wait to get to a vet, the more harm and long-lasting illness will occur! Do that then read the rest of this later!
Phena-S can cause seizures in dogs, and death. They need veterinary care as soon as possible, and a liquid charcoal concoction to absorb any poison left in the stomach.
Here is a site that may help with future instances of your pups getting into things:
I hope this helps, and I hope I wan't too late! Good luck!