Bamboo scrimber (BS) has been widely used as a high-performance engineering composite in construction and outdoor applications, typically employing a thermosetting adhesive that requires hot-pressing. Previous studies have focused on the effects of resin content and BS curing temperature, often overlooking the self-bonding of bamboo during the hot-pressing process. This study investigated the impact of hot-pressing temperature and density on the physical and mechanical properties of BS containing phenol–formaldehyde resin, with a particular focus on regulating BS self-bonding by adjusting these parameters. The study also examined the effects on the chemical composition and pore structure of BS. The results showed that increasing the hot-pressing temperature from 140 to 180 °C broke unstable bonds in the hemicellulose, cellulose, and lignin components of the BS, leading to new crosslinks through dehydration and thermal degradation reactions. This process enhanced self-bonding, improved water resistance, and resulted in different surface colors. Raising the density from 0.9 to 1.3 g/cm3 made the density distribution of BS more uniform and reduced the size and number of internal pores. These characteristics promoted interfacial bonding and impeded water flow through the material, thereby enhancing its water resistance and mechanical properties. This study elucidates the mechanism behind the performance enhancement of BS and offers insights for its low-cost and environmentally friendly production.