High‐brightness laser lighting is confronted with crucial challenges in developing laser‐excitable color converting materials with effective heat dissipation and super optical performance. Herein, a novel composite of phosphor‐in‐glass film on transparent diamond (PiGF@diamond) is designed and fabricated via a facile low‐temperature co‐sintering strategy. The as‐prepared La3Si6N11:Ce3+ (LSN:Ce) PiGF@diamond with well‐retained optical properties of raw phosphor shows a record thermal conductivity of ≈599 W m−1 K−1, which is about 60 times higher than that of currently well‐used PiGF@sapphire (≈10 W m−1 K−1). As a consequence, this color converter can bear laser power density up to 40.24 W mm−2 and a maximum luminance flux of 5602 lm without luminescence saturation due to efficient inhibition of laser‐induced heat accumulation. By further supplementing red spectral component of CaAlSiN3:Eu2+ (CASN:Eu), the PiGF@diamond based white laser diode is successfully constructed, which can yield warm white light with a high color rendering index of 89.3 and find practical LD‐driven applications. The findings will pave the way for realizing the commercial application of PiGF composite in laser lighting and display.