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Orthogonal frequency division multiplexing (OFDM) is an effective modulation scheme to improve the performance of a communication system over wireless multipath fading channels. However transceiver hardware non-idealities combined with channel limits the performance. In this paper we study the effect of local oscillator phase noise in slow time varying channels considering realistic phase noise power spectral density (PSD) function. Carrier to Interference ratio (C/I) expression for individual subcarrier is derived for the additional intercarrier interference (ICI) due to the joint effect of Doppler and phase noise. Realistic phase noise PSD and Jakes Doppler PSD are used to quantify these OFDM system performance metrics. Analytical expression of upper bound on the system performance is obtained. Unlike Gaussian time invariant channels, in time varying channels, OFDM system performance is upper bounded by the ICI due to joint effect of Doppler and phase noise rather than Doppler alone. Numerical and simulation results are included which supports these derived theoretical results.