I want to store Complex Displacement Vector in PointData. For each point, there is Magnitude and Phase value of displacement(T) in X(T1),Y(T2) and Z(T3) axis. What is the format? Is it:
T1Mag,T1Phase,T2Mag,T2Phase,T3Mag,T3Phase

Or

T1Mag,T2Mag,T3Mag,T1Phase,T2Phase,T3Phase

Or is it depends on what software is used to open it? I want to use Paraview.

If you want to store complex values, you should use them as 2D vectors (x, y) such that z = x + i y. Complex numbers are not very well handled in VTK or ParaView, so what you are dealing with when you do that is just a plain 2D vector.

If you need to be able to do operations on those complex numbers in C++, I would advise implementing them somewhere in your program and use them. You can find an example of some complex number operation implementation at the beginning of the header Imaging/Fourier/vtkImageFourierFilter.h in the VTK repo.

Edit:
So in your point data, you would have X1, Y1, X2, Y2...