Excessive Mucus/Phlegm can be caused due to a number of conditions. It is usually due to an irritation in the lungs, sinus, nose and throat and respiratory tract. So you do need to eliminate if there is any infection first. Mucus is designed to protect the lining's of these areas from drying out so it is important to make sure, and especially for PDr's, that you are well hydrated by drinking water, tea (especially green tea) regularly throughout the day. This helps thin out the mucus/phlegm and also is necessary for other PD symptoms However do not drink soda/fizzy drinks at all as they are very high in sugar. Other things that can cause phlegm are dairy products such as cows milk, yogurt, cheese so try eliminating these from your diet. Use alternatives such as almond or rice milk.
This has helped me a lot in reducing sinus/nasal mucus. Spicy foods can also be a cause.
Something I do every night is use a nasal irrigator/sinus rinse (Neilmed Brand). to clear the nasal passages, and sometimes in the morning as well. You could also try gargling your throat with a teaspoon of salt in a glass of water to help clear out the throat and the throat pocket that many older people, especially men, get just below the adams apple. Try inhaling a few drops of Eucalyptus Oil in a hot basin of water. Put a towel over your head and deep breath in.
You could also ask your doctor about taking Mucinex.
Hope this gives you something that might help.
Hugs
Brent

Thanks for the advice and information. Brent.

I would DEFINITELY be in contact with my primary care doctor, along with getting on the portal to see what my neurologist has to say about this!!!

My hubby as Kleenex by him always. It’s there when he’s able to cough up that phlegm.

Good advice!