  We investigate the influence of laser phase noise heating on resolved
sideband cooling in the context of cooling the center-of-mass motion of a
levitated nanoparticle in a high-finesse cavity. Although phase noise heating
is not a fundamental physical constraint, the regime where it becomes the main
limitation in Levitodynamics has so far been unexplored and hence embodies from
this point forward the main obstacle in reaching the motional ground state of
levitated mesoscopic objects with resolved sideband cooling. We reach minimal
center-of-mass temperatures comparable to $T_{min}=10$mK at a pressure of $p =
3\times 10^{-7}$mbar, solely limited by phase noise. Finally we present
possible strategies towards motional ground state cooling in the presence of
phase noise.
