To fully utilize the straight section space and achieve higher brightness, two beamlines in the first phase of the High Energy Photon Source (HEPS) adopt a tandem layout of double cryogenic permanent magnet undulators (CPMU), with a phase shifter employed between the two CPMUs to match the optical phases. However, limited by the diameter of the vacuum bellows, the operating gap of the HEPS phase shifters is relatively large, resulting in oversized permanent magnets and imposing higher requirements on the structural design and assembly methods of the phase shifters. After magnet blocks assembling, demagnetization of the permanent magnet material was observed; nevertheless, magnetic field tuning was successfully completed under these conditions. This paper presents a comprehensive introduction to the design, fabrication, and testing of the HEPS phase shifters.