Phase tensor is defined by the 4 angles, computed from 4 impedance components Zxx, Zxy, Zyx, Zyy as:
Chave, A.D. and Jones, A.G. eds., 2012. The magnetotelluric method: Theory and practice. Cambridge University Press.
Wight, D.E., 1987. Society of Exploration Geophysicists MT/EMAP Data Interchange Standard.