I don't have direct experience with it, but could be kennel cough...basically equivalent to the human cold or flu. I don't know if that produces a lot of phlegm though....
If they don't have a vet here yet could you find a vet near you to take him to? You sound very worried about the little guy and I think a vet would be the best able to help. Good luck, and please let us know what the vet says!
Chase (Friendly Resident Wigglebum) - Border Collie/Lab/Shepherd X
Kailey (Misunderstood Gentle Beauty) - GSD & foster failure #1
Rupert (Gold-Medal Winner of the 3 a.m. Kitty Destruction Olympics
Heidi - RIP my sweet baby girl