  We consider the problem of monostatic radar sensing with orthogonal
frequency-division multiplexing (OFDM) joint radar-communications (JRC) systems
in the presence of phase noise (PN) caused by oscillator imperfections. We
begin by providing a rigorous statistical characterization of PN in the radar
receiver over multiple OFDM symbols for free-running oscillators (FROs) and
phase-locked loops (PLLs). Based on the delay-dependent PN covariance matrix,
we derive the hybrid maximum-likelihood (ML)/maximum a-posteriori (MAP)
estimator of the deterministic delay-Doppler parameters and the random PN,
resulting in a challenging high-dimensional nonlinear optimization problem. To
circumvent the nonlinearity of PN, we then develop an iterated small angle
approximation (ISAA) algorithm that progressively refines delay-Doppler-PN
estimates via closed-form updates of PN as a function of delay-Doppler at each
iteration. Moreover, unlike existing approaches where PN is considered to be
purely an impairment that has to be mitigated, we propose to exploit PN for
resolving range ambiguity by capitalizing on its delay-dependent statistics
(i.e., the range correlation effect), through the formulation of a parametric
Toeplitz-block Toeplitz covariance matrix reconstruction problem. Simulation
results indicate quick convergence of ISAA to the hybrid Cram\'{e}r-Rao bound
(CRB), as well as its remarkable performance gains over state-of-the-art
benchmarks, for both FROs and PLLs under various operating conditions, while
showing that the detrimental effect of PN can be turned into an advantage for
sensing.
