Earlier quoted context omitted.
Dairy products do not cause an increase in mucus production but can cause a thickening of phlegm [0] [0]: https://www.mayoclinic.org/diseases-conditions/common-cold/e... (there are numerous studies supporting the lack of an increase in mucus due to dairy which can be found by searching "milk mucus increase")
This statement is a bit confusing; "Phlegm is a slightly different substance. It's a form of mucus produced by the lower airways — not by the nose and sinuses — in response to inflammation. You may not notice phlegm unless you cough it up as a symptom of bronchitis or pneumonia;" searched "mucus vs. phlegm" on Google. Therefore isn't a thickening of phlegm (a form of mucus) an increase in quantity, therefore we can s…
> Therefore isn't a thickening of phlegm (a form of mucus) an increase in quantity, therefore we can say it increases?
I don't necessarily agree with this. You can change the viscosity of water by adding gelatin, but you didn't add more water to make it thicker.
But I am most certainly not a doctor and I realize I have no idea what exactly phlegm is!