Polycrystalline samples La2 − xSrxCuO4 − δ(0.06 ≤ x≤ 0.5) and La1.85 − xSr0.15 + xCu1 − xCoxO4 − δ(0 ≤ x≤ 1) were synthesized by a conventional solid state reaction method. The structure, phonon vibration, and conduction were investigated by means of XRD, infrared (IR) spectra, and resistance. It is found that the increase of itinerant hole carriers could mask the in-plane $${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$$ stretching vibration mode (689 cm−1). The softening of the $${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$$ phonon vibration mode gives an index of the weakening of $${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O}}$$ hybridization. The distortion of CuO6octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.