The noise floor of the CY2304NZ is lower than any reference source we have, so phase noise must be measured in a two-port (residual) manner, where the E5500 measures the phase noise of the difference between the input and output signals. Above 1 MHz offset, the curve increases because the delay of the two paths was not fully matched. In reality it is most likely flat.
Attached is CY2304NZ Residual Phase Noise at 80MHz
