L. Mohan,

Give us more details and context.

Generally, phase angle changes with frequency, as part of any frequency-dependent system or function or filter. Additionally, a time delay causes a phase shift that is linearly proportional to frequency.

When you say 120 degrees, is that a constant phase shift, i.e. , not changing with frequency? How do you construct the Bode plot? What are the data?

Cecil Thomas

As our friend said, it dependents many parameter. One thing is the order of your system. How far are the pole and zeros from each other and from jw axis if you use definite system model? If you use frequency-response data model, what is the range of you stimuli frequencies? give us more detail please