The representation of the glottal source is of paramount importance for describing para-linguistic information carried through the voice quality (e.g., emotions, mood, attitude). However, some existing representations of the glottal source are based on analytical glottal models, which assume strong a priori constraints on the shape of the glottal pulses. Thus, these representations are restricted to limited number of voices. Recent progresses in the estimation of the glottal models revealed that the Phase Distortion (PD) of the signal carries most of the information about the glottal pulses. This paper introduces a flexible representation of the glottal source - based on the short-term modelling of the phase distortion. This representation is not constrained by a specific analytical model, and thus can be used to describe a larger variety of expressive voices. We address the efficiency of this representation for the recognition of various voice qualities, with comparison to MFCC and standard glottal source representations.