The best thing for phlem is cayenne tincture, as Shelley would say "at least 10 000 heat units"
I found this detoxifying drink Shelley recommends, and perhaps you could give it to your Dad to get rid of congestion...
It's something like:
1 Tbs Apple Cider Vinegar (Bragg's)
1 Tbs molasses or Maple Syrup
4-5 drops of Cayenne Tincture
Mix in 8-12 oz water
If you can't get to the health food store, if you have Tabasco , put 10 drops in a glass of warm water.
Give plenty of fluids (warm lemonade made with lots of lemon juice and honey is good)
Also, check Shelleys site for the detox and rehuydration drink, and I think there is a post about what to do in case of flu/cold symptoms.
God bless you and your Dad...:)