The electron-phonon (e-ph) coupling systems usually have large phonon degrees of freedom, whose spectral functions are numerically difficult to compute using matrix product state (MPS) formalisms. For the first time, we propose a simple and practical method that combines the Chebyshev MPS and the pseudosite density matrix renormalization group (DMRG) algorithm. The Chebyshev vector is represented by a pseudosite MPS with global U (1) fermion symmetry, mapping 2 Np bosonic degrees of freedom to Np pseudosites, each with two states. This approach can handle arbitrary eph coupling Hamiltonians where pseudosite DMRG performs efficiently. We employ this method to investigate the spectral functions of the doped extended Hubbard-Holstein model, concentrating on a rarely studied strong Coulomb repulsion regime. We show that even weak extended electron-phonon couplings have non-negligible effects on spectral functions. With this method, key features of the excitation spectra for the extended Hubbard-Holstein model are captured at a modest computational cost.