Organic materials with persistent room-temperature phosphorescence (pRTP) have attracted great attention for their wide applications in display, sensing, and bioimaging. However, manipulation of the emission properties of organic phosphors is challenging, requiring intricate molecular design and tedious synthesis processes. Herein, we develop a simple and versatile strategy for achieving tunable pRTP by modulating the size of anionic aromatic phosphorescent cores and cations in organic salts. Remarkably, pairing large phosphorescent cores with larger-sized guanidinium ions, rather than smaller potassium ions, enables bright pRTP. Meanwhile, pairing small phosphorescent cores with guanidinium ions yields a blue-shifted but longer-lived pRTP compared to those paired with potassium ions. Mechanistic studies reveal that large cations primarily weaken π-π interactions, thereby reducing triplet quenching in large phosphorescent cores, while causing a blue shift in both excitation and emission wavelengths in small phosphorescent cores. Through a simple and reversible cation-exchange process, organic salts capable of excitation-dependent color (from blue to green) and lifetime (from 0.86 s to 1.28 s) tunable pRTP can be achieved, which allows advanced applications in multiple afterglow anti-counterfeiting and dynamic information encryption.