Lips deliver visually active clues for speech articulation. Affective states define how humans articulate speech; hence, they also change articulation of lip motion. In this paper, we investigate effect of phonetic classes for affect recognition from lip articulations. The affect recognition problem is formalized in discrete activation, valence and dominance attributes. We use the symmetric Kullback-Leibler divergence (KLD) to rate phonetic classes with larger discrimination across different affective states. We perform experimental evaluations using the IEMOCAP database. Our results demonstrate that lip articulations over a set of discriminative phonetic classes improves the affect recognition performance, and attains 3-class recognition rates for the activation, valence and dominance (AVD) attributes as 72.16%, 46.44% and 64.92%, respectively.