Other than allergies, what else can cause me to have a hoarse voice for an hour? (sounding like i had phlegm in my throat, but can't clear it)

Many things: There are many things that can give you hoarseness. Allergies certainly. Other things to consider: gastric reflux, straining your voice, infections (viral usually), irritants like chemicals and alcohol, the use of steroid-based inhalers in asthma, vocal cord polyps, vocal cord dysfunction, etc.

The mucus in your: Throat is causing the hoarseness . You would need a decongestant with guaiafenesin combination to help clear your throat.Drink plenty of warm liquids, warm honey lemon tea, adding ginger will help.Consult your doctor if you need prescriptions or if you are not any better.

Reflux: If you have recurrent hoarseness, post nasal drp with a clear nose, acid and or nonacid reflux disease could be a cause. People with this problem are frequently clearing their throat.