What is the best OTC medicine for mucous/phlegm in the chest and an overall ache/headache?

Mucinex or Robitussin is best for getting that phlegm loosened up. Drinking lots of water helps too. The headache and general soreness are commonly seen in flu and other viral infections. Rest and fluids is best medicine. If sore throat or fever or worsening of current symptoms occur, I would consult your physician for treatment. I'm a clinical pharmacist.