An analysis of the phase spectrum of the DA pulsating white dwarf G29–38 over many seasons has been performed. This complements a companion paper which analyses the evolution of the temporal spectrum of G29–38.

We show that, with one exception, the relative phases of the harmonics and combination frequencies are all oscillating in phase with their parent modes. This not only suggests that these non-linear frequencies owe their presence to harmonic distortion and not to resonant mode coupling, but also explains the typical pulse shapes observed in the light curves of large-amplitude variable white dwarfs.

The one exceptional cross-frequency that does not show a phasing with its parent modes is thought to be a resonance.