  The structural and vibrational properties of phenanthrene are measured at
high pressures up to 30.2 GPa by Raman spectroscopy and synchrotron x-ray
diffraction techniques. Two phase transitions are observed in raman spectra
under pressures of 2.3 GPa and 5.4 GPa with significant changes of
intermolecular and intramolecular vibrational modes, and all the raman peaks
disappeared in the luminesce background above 10.2 GPa. Upon further
compression above 20.0 GPa, three broad bands are observed respectively around
1600, 2993 and 3181 cm$^{-1}$ in Raman spectra, strongly indicating that
phenanthrene has transformed into amorphous hydrogenated carbon. Based on x-ray
diffraction, the structures of corresponding phases observed in Raman spectra
are identified with space group of $P_{\rm}2_{1}$ for phase I at 0-2.2 GPa,
$P_{\rm}$2/\emph{m} for phase II at 2.2-5.6 GPa and
$P_{\rm}$2/\emph{m}+\emph{Pmmm} for phase III at 5.6-11.4 GPa, and the
structure above 11.4 GPa is identified with space group of \emph{Pmmm}.
Although phenanthrene has amorphized above 20.0 GPa, the amorphous hydrogenated
carbon clusters still remain the crystalline characteristic based on x-ray
diffraction patterns. Our results suggest that the long-range periodicity and
the local disorder state coexist in phenanthrene at high pressures.
