<p>Higher-order hyperbolic phonon polaritons (HoHPhPs), arising from photon–phonon coupling under geometric confinement and resonance conditions, exhibit larger wavevectors, field confinement and tunability compared with fundamental hyperbolic phonon polariton (HPhP) modes, making them promising for compact nanophotonic devices. However, their excitation remains challenging due to stringent momentum compensation requirements, leaving their properties and applications largely unexplored. Here we overcome this challenge by introducing a boundary-induced scattering mechanism that facilitates the efficient stepwise excitation of HoHPhPs. By creating a high-contrast dielectric environment with a gold–air hybrid substrate, we achieve substantial momentum compensation through scattering at the gold edge. Our approach is validated by theoretical analysis using dyadic Green’s function theory, demonstrating more than a sixfold increase in the excitation efficiency of HoHPhPs compared with conventional antenna-launching of HPhP. Experimentally, we observe HoHPhPs in α-MoO₃ layers with a propagation distance of up to 15.2 μm and report a pseudo-birefringence effect with an ultrahigh equivalent birefringence ranging from 17.6 to 41.8. Thus, different polariton orders are spatially separated by their propagation direction without altering their polarization state. Our work introduces a novel strategy for the efficient excitation of HoHPhPs and establishes them as a versatile platform for nanophotonic applications such as mode routing in nanocircuits.</p>