What stage is it?

Phase refers to the time relationship between two or more periodic waveforms. At the same time, the phase angles of different waveforms can be different, indicating that their waveform shapes are different. In sine waves, the unit of phase angle is radian. The importance of phase is that it plays an important role in wave theory and signal processing, and it is used to describe the change of waveform and the interaction between waveforms.