This standard is a key method for determining the pH value of phenolic resins used in plastics. Its core principle involves measuring the potential difference between a glass electrode and a reference electrode immersed in a phenolic resin solution to determine the pH value. This standard is primarily applicable to conventional liquid phenolic resins. For high-viscosity liquids (such as those with a viscosity greater than 2 Pa·s) or solid resins, a specific testing method is provided in Appendix A. The essential instrument required for this test is a pH meter (also known as an acidity meter), commonly used in laboratories, with the explicit requirement to use a combination electrode and corresponding standard buffer solutions for calibration and measurement. It provides a unified and scientific technical basis for evaluating the acidity or alkalinity, stability, and subsequent processing and application performance of phenolic resins.