Longitude-resolved phase angle spectra of the Q-mode (top) and the B and Bf-mode (middle). The LRPS visualises the phase relationship between different fluctuation frequencies in the pulsar’s emission, in contrast to the LRFS, which shows their magnitudes. The FFT block size was set to 8000 and 1680 rotations, corresponding to eight and four times oversampling. Bottom: phase angle gradient along the frequency axis of the Q-mode LRPS from the top panel. We zoomed into the area near the P₃ = 41.7 P₁ modulation feature shown with a star marker.