Guaifenesin/Phenylpropanolamine - is it a antibiotic?

No, both the ingredients are not antibiotics.

Guaifenesin is an expectorant. It is used to break up congestion and mucous to make breathing easier. Guaifenesin thins mucous, increases lubrication of the respiratory tract (lungs, nose and throat), and increases the removal of mucous.

Phenylpropanolamine is a decongestant. It constricts (shrinks) blood vessels (veins and arteries), which reduces swelling of mucous membranes in areas such as the nose and sinuses.

Guaifenesin and phenylpropanolamine is used to treat the symptoms of the common cold and of infections of the sinuses, lungs, and throat.

http://www.drugs.com/mtm/guaifenesin-and-phenylpropanolamine.html