from the point of view of electrical engineering, the behavior of this circuit is obvious. But I gues it's an equivalent circuit diagram for biological tissue or something similar which I'm not familiar with, and I cannot recognize anything causing a constant phase. (At f = 0 Hz and at f -> infinity, phi = 0, but between these extremes, phi is changing within the limits 0 and pi/2.)
So, could you please give a link to an explanation of the context of your question resp. to a relevant chapter of a textbook?