Hello,
The hoarsness of voice could be because of the singing vigourously, but the phlegm could not be explained on it.
You might have nasal infections or allergic secretions which are coming in the back of throat and causing irritation or it could be reflux disease.
You need to take care of two things
1. nasal allergies / disease like blockage,discharge etc if you have,,,, as the nasal discharge fall back in throat and irritates it.
you need to consult your
ENT specialist to get examination and
CT scan nose with plain coronal views limited cuts,, if required to rule out any disease in nose and
paranasal sinuses 2. Take care of reflux, It is one of the reason for recurrent
throat irritation ,, it doesnot matter you feel heart burn acidity or not.
Take--- Antacids and antireflux medicines .
Precautions—
Keep head end of bed elevated.
Avoid alcohol, Smoking
Do brisk walking daily
Go for walk after dinner
Avoid spicy food
Avoid late night coffee