(a) Velocity Fourier phases ϕ₂₁ for first-overtone and short-period fundamental-mode Cepheids. Red labels correspond to overtone Cepheids for which our results disagree either with the Gaia SOS Cep&RRL pipeline or with reclassification by (Ripepi et al. 2023) (see Table 2). Purple symbols correspond to stars with uncertain or unknown pulsation mode according to our criteria based on ϕ₂₁. V1726 Cyg and GH Lup cannot be plotted because the second Fourier term has not been detected in these stars, and V636 Cas has very high ϕ₂₁ ≃ 4.5 rad. (b) Astrometry-based luminosities in the Wesenheit G-band for selected stars of Fig. 7a. Relations for the first-overtone and fundamental-mode Cepheids are also plotted as red and black curves, respectively.