The practical application of carbon dots (CDs) in room-temperature phosphorescence (RTP) is fundamentally constrained by the inherent trade-off between phosphorescence lifetime and quantum yield within conventional single-confinement systems. Herein, we report a multiscale-coupled triple-confinement paradigm that integrates molecular-level covalent locking (C=N bonds), nanoscale silica encapsulation, and matrix-level boron oxide rigidification. This synergistic design decouples the competing requirements of enhanced intersystem crossing (ISC) and suppressed nonradiative decay, enabling nonlinear performance amplification with a synergy index S = 2.4 (> 1). The optimized CD@SiO₂@B₂O₃ composite exhibits an exceptional phosphorescence lifetime of 1119.8 ms and a quantum yield of 25.98%, corresponding to 3.8-fold and 1.7-fold enhancements relative to single-confinement CD@B₂O₃ (291.4 ms and 15.35%), respectively. Systematic mechanistic investigations confirm that C=N bonds reduce the singlet-triplet energy gap (ΔE_ST) by 0.14 eV to facilitate ISC, whereas the hybrid matrix suppresses nonradiative decay rate by 77.2% (from 2.90 to 0.66 s⁻¹). This strategy is readily extendable to other systems and exhibits excellent universality. Furthermore, leveraging phosphorescence resonance energy transfer (PRET) with trace amounts (1 wt.%) of fluorescent dyes enables multicolor RTP tunability while preserving hundreds-millisecond lifetimes, overcoming the emission color restriction of traditional RTP CDs. These merits enable applications including time-gated information encryption with second-level temporal resolution, high-contrast fingerprint visualization on multicolor substrates, and warm-white light-emitting diodes (LEDs) free of commercial phosphors. This work establishes a universal design principle for multiscale-coupled confinement, providing a robust platform for next-generation high-performance RTP materials.