Is pharyngitis really serious or common and can be easily cured ?

Depends: Pharyngitis means inflammation of the pharynx causing a sore throat. If the sore throat is caused by a virus it can be easily cured. If the sore throat is caused by throat cancer it is really serious and needs serious treatments which may include chemo, radiation, surgery etc. So a sore throat that does not go away after a few weeks should be evaluated by a doctor.