Contribution of phase noise to the total noise in our ALMA observations (Ruge, priv. comm.). The noise levels are computed as the standard deviation of all pixels in simulated observations of empty images (all pixels set to 0.0). The quantity σ_th represents the standard deviation in simulations with only thermal noise considered, while σ_th + ph is derived from simulations considering thermal and phase noise. Ratios higher than 1.0 may occur because of uncertainties in noise estimates and because of different noise contributions that in part cancel out each other. The curves for Band 5 and Band 6 are very close to 1.0 and cannot be distinguished in the plot. In any case, the contribution of phase noise is lower than 5%.