Short answer
Section insulators are governed by the industry standard TB/T 3036-2016 "Section insulators for electrified railway overhead contact systems" (current edition, effective 16 February 2017); phase insulators by TB/T 3037-2002 "Phase insulators for 25kV electrified railway overhead contact systems". General technical requirements for both are taken from the TB/T 2075 series (current 2024/2026 editions).
How the two differ
A section insulator provides an electrical section break inside one feeding section (station throat areas, loading tracks, depot tracks), with the same phase on both sides. A phase insulator is installed at the electrical neutral section between feeding sections of different phases, has to withstand the voltage difference between two phases, and the train coasts through with power off. In construction the phase insulator carries more insulating parts and a larger air gap.
Related products and reading
Section insulator series | Phase insulator series | Section insulator vs phase insulator: the detailed difference | Section insulator model selection guide