Anna,
The glands in your nose and throat continually produce mucus (1-2 quarts per day). It moistens and cleans the nasal membranes, humidifies air, traps and clears inhaled foreign matter, and fights infection. Although mucus is normally swallowed unconsciously, the feeling that you have a "constant phlegm in throat" issue is caused by the same throat mucus that causes post nasal drip.
Excess throat mucus can occasionally cause irritation and even slight bleeding. It can also cause bad breath as it is high in proteins and is an excellent food source for anaerobic bacteria. Once this throat mucus settles on your nasal and throat lining, it can irritate, causing that constant phlegm in throat feeling, and can trick you into thinking that you may be coming down with a cold or some other problem.
I would not wait until you are having a anxiety attack and go to the ER but I would suggest you see your physician and discuss your problem to rule out a medical reason for the phlegm.
GERD sometimes causes excess phelgm as well as other problems.
If you wait until you are in panic mode and go to the ER they will treat the panic and you will still have the issue of what is causing the excess phlegm.
Take care and keep us posted on how you are doing.
Kitt