Sine of the signal in Xilinx Simulink

Question

I am implementing a DQPSK modulator and Demodulator. I would like to calculate the exp(1j*Phase) in Simulink.

How can I realize such a model ?

Here is the part of the model to calculate the Phase:

Any help in this direction, would be highly appreciated.

BTW, ROM3 block in the model stores the values: 0, pi/2, pi, 3*pi/2 ( Constellation points)

Thanks for reading, Kiran