This paper investigates the use of the phase angle of the measured speed harmonics for efficient permanent magnet (PM) temperature estimation of permanent magnet synchronous machine (PMSM). Based on the mechanical model, a linear estimation model is derived to model the relationship between the PM temperature and the phase angle of the speed harmonic. This model shows that there is a linear relationship between the PM temperature and the tangent of the phase angle. Therefore, the PM temperature can be directly estimated from the phase angle of the speed harmonic using the derived model. Moreover, the derived estimation model does not involve machine parameters such as inductance and winding resistance, thus the proposed estimation approach is independent from machine parameter variation. The proposed approach is evaluated on a laboratory interior PMSM.