At least two explanations can be offered for the monaural phase effects reported in previous tone‐on‐tone masking experiments. The aural distortion approach leads to the prediction that changes in the phase angle between masker and maskee will cause sensitivity variations only at harmonic intervals. The two‐tone interaction approach suggests that phase effects should also be evident at nonintegral multiples of the masker. To test these predictions, six normal listeners traced their thresholds at 1500, 2000, and 2500 Hz in the presence of a 1000‐Hz masker at each of five intensities: 50–90 dB SPL in 10‐dB increments. Within each session, the phase was shifted in randomly ordered 60° steps through one complete period (of the maskee). When confusions due to a 500‐Hz difference tone are avoided by including a narrow‐band (270–510 Hz) masking noise, no phase effects are evident at 1500 and 2500 Hz. The thresholds for the 2000‐Hz maskee, however, show the usual phase dependencies. These findings are inconsistent with the two‐tone interaction explanation and support the interpretation that emphasizes nonlinear response of the auditory system and direct interference between the aural and acoustic harmonics. Furthermore, when estimates of the second aural harmonic are obtained, its magnitude appears to vary directly withf1intensity at the 2 dB/dB rate predicted from the power law description of amplitude distortion.