dark (yellow) phlegm could be a sign of an infection or at least stagnation of mucous in your nose sinuses or lungs. the fact that it is foul-tasting is another sign of a possible infection. the color of mucous is not as important is the entire package of symptoms that you may be experiencing so if this continues you may need to see a medical evaluation. in the meantime drink plenty of water (this will thin your mucous) humidify the air (humidifier or a hot steamy shower) and consider trying a decongestant during the day. if the underlying cause is a cold (viral) then you should be improving in a few days. if you are having sinus pain sore throat chest pain or fever then it would not be prudent to wait it out.
i am spittimg up yellow stuff. i start coughing and i cough up yellow stuff. my mouth then taste like i have eaten soething that was scorched.