  Anisotropic hyperbolic phonon polaritons (PhPs) in natural biaxial hyperbolic
material MoO$_3$ has opened up new avenues for mid-infrared nanophotonics,
while active tunability of $\alpha$-MoO$_3$ PhPs is still an urgent problem
needing to be solved.In this study, we present a theoretical demonstration of
actively tuning $\alpha$-MoO$_3$ PhPs using phase change material VO$_2$ and
graphene. It is observed that $\alpha$-MoO$_3$ PhPs are greatly depending on
the propagation plane angle of PhPs. The metal-to-insulator phase transition of
VO$_2$ has a significant effect on the hybridization PhPs of the
$\alpha$-MoO$_3$/VO$_2$ structure and allows to obtain an actively tunable
$\alpha$-MoO$_3$ PhPs, which is especially obvious when the propagation plane
angle of PhPs is 90.
