I also feel like i need to spit out phlegm?

Many issues. Unclear for how long the symptoms have been going on. If you are new to high altitude you can experience headache and upper respiratory symptoms as there is a syndrome called high altitude sickness. F/U/w MD today https://www.webmd.com/a-to-z-guide Also get COVID /flu /strep tested If has been a while may be allergies , sinusitis, w/ migraine or reflux/ H pylori. F/u/w/ MD