As phlegm is pure and is not food or drink, and does not come under the same rulings as food and drink, if a person swallows while praying, the prayer remains valid, especially if one could not help it and was not able to spit it out into a handkerchief and the like.

1- There is nothing wrong with praying on a prayer mat, regardless of whether it is made of rags, palm leaves or anything else, whether it is small or big, like a mat or carpet. 2- It is proven that the Prophet (peace and blessings of Allah be upon him) prayed on mats, carpets and animal pelts.