In order to reduce the size of endoscopic imaging probes to accommodate more usage environments and to achieve high-resolution ultrafine endoscopic imaging，an experimental study is conducted on a scanless，lensless，flexible optical endoscopic phase imaging technique based on coherent fiber bundles（CFB）. An imaging experimental setup is established using a 1 550 nm single-frequency narrow linewidth laser，a CFB，and a high-speed short-wave infrared camera. Point-target imaging experiments are carried out. The impact of the phase error introduced by the inconsistent length of the coherent fiber bundle on the imaging and the compensation method is studied，and a theoretical modeling analysis is carried out. The experimental results show that the phase error introduced by the core length of the coherent fiber bundle is relatively stable during the observation time of up to 5 hours，and can be effectively compensated. At the 10 cm away from the distal facet of the coherent fiber bundle，the phase error compensation can be achieved within the transverse shift of the point target of ±4 mm，but with the increase of the transverse shift of the point target，the phase error compensation becomes worse or even fails completely. Theoretical analysis and simulation results show that the angular correlation of phase error compensation is related to the multimode propagation of the optical field in the coherent fiber bundle，and the use of pure single-mode transmission of the coherent fiber bundle or the fine grinding of the two end faces of the coherent fiber bundle to eliminate the core length error can suppress the angular correlation of the phase error compensation and achieve effective compensation.