A 45 years old man presents with hoarseness for 5 days, cough, and pain on swallowing. He has no fever but complains of increased mucus in his throat and occasional difficulty breathing. He has no prior history of hoarseness, surgery to the larynx, intubation, or vocal abuse. He has slight throat pain but denies reflux symptoms. On examination, there is no acute respiratory distress. His oral cavity is within normal limits, but the oropharynx shows hyperemia. The tonsils are slightly enlarged and erythema. Mirror examination of the larynx reveals diffuse edema and erythema of the laryngeal structures, with increased mucus in the glottis, but the airway is patent. What is the most likely diagnosis?