<p>Diamond-like (DL) structure facilitates optimal superposition of the second-order polarizability in tetrahedra, rendering it a widely adopted template for nonlinear optical (NLO) crystals. DL phosphides, serving as potential employers for infrared (IR) NLO materials, have persisted in an underdeveloped state for a considerable duration due to the difficulty of synthesis. In this work, we strategically opted for the [Sr₄Br] tetrahedra and [Ba₂Sr₄Br₂]_∞ chain as polycations, leading to the successful formation of two novel salt-inclusion phosphides featuring DL anionic frameworks: [Ba₂Sr₄Br₂][Sr₄Br][In₅Si₃₁P₅₂] (<b>1</b>) and [Sr₄Br][In₂Si₁₁P₁₉] (<b>2</b>). Both phosphides exhibit the remarkable structural characteristics of T3-supertetrahedra, which is rarely observed in IR nonlinear optical (NLO) crystals. Interestingly, a tenfold enhancement in the intensity of phase-matching second-harmonic generation (SHG) is observed in phosphide <b>2</b> (2.1 × AgGaS₂) compared to that in <b>1</b> (0.2 × AgGaS₂), which can potentially be attributed to the significant distinct distorted degrees and stacking methods demonstrated by [InP₄], [SiP₄] and [In/SiP₄] tetrahedra impacted by polycations. Additionally, both phosphides <b>1</b> and <b>2</b> display moderate optical bandgaps (1.70 and 1.87 eV), large laser-induced damage thresholds (LIDT, 6.0 and 5.0 × AGS@2090 nm), and excellent infrared transparency. The present study provides a novel avenue for the flourishing development of diamond-like structures and salt-inclusion phosphides.</p>