This study investigates two-dimensional phonon transport in supported graphene. The thermal conductivity (κ) of monolayer graphene exfoliated on a silicon dioxide support is found to be about 600 W m⁻¹ K⁻¹ near room temperature, which is higher than that of common thin-film electronic materials but lower than that of suspended graphene. The lower κ in supported graphene is attributed to phonon leakage across the graphene-support interface and strong interface scattering of flexural modes, which are significant contributors to κ in suspended graphene. Graphene, first exfoliated from graphite in 2004, has attracted attention for its superior charge mobility and mechanical strength. Other carbon allotropes, including diamond, graphite, and carbon nanotubes, have high thermal conductivity due to strong bonding of light carbon atoms. Graphene is expected to have a much higher thermal conductivity than silicon active layers and copper interconnects in current electronic devices, potentially solving heat dissipation problems in nanoelectronics. Despite extensive research on electronic transport in graphene, thermal transport has been less studied due to experimental challenges. Recent studies have reported room-temperature κ of suspended single-layer graphene (SLG) as high as 3000-5000 W m⁻¹ K⁻¹, exceeding those of diamond and graphite. However, the κ-T relation is not well understood. SLG is usually supported on a dielectric substrate for device applications, and substrate interaction affects thermal transport. The study reports thermal transport measurements on SLG supported on amorphous SiO₂, which is the most common device configuration. Despite phonon-substrate scattering, the room-temperature κ of supported SLG is found to be about 600 W m⁻¹ K⁻¹, significantly higher than common thin-film materials. Using quantum mechanical calculations, the study finds that flexural (ZA) modes contribute significantly to κ in suspended SLG. The measured κ-T relation is explained by the suppression of ZA contribution in supported SLG. The study measures the thermal conductivity of three SLG flakes exfoliated onto SiO₂. The results show that the κ of supported SLG is about 3.4 times lower than the highest reported basal-plane value of pyrolytic graphite. The κ-T curve for supported SLG shows a peak at a much higher temperature than that of PG, indicating that phonon scattering is dominated by substrate interaction and umklapp scattering. Theoretical analysis suggests that the ZA contribution to κ is large in suspended SLG, and the measured κ-T relation can be explained by stronger substrate scattering of ZA phonons than LA and TA phonons. The study also shows that graphene exfoliated on SiO₂ still conducts heat efficiently despite phonon-substrate interaction. However, the substrate effect could be different for few-layer graphene or SLG grown on other substrates. These findings highlight the importance of understanding phonon transportThis study investigates two-dimensional phonon transport in supported graphene. The thermal conductivity (κ) of monolayer graphene exfoliated on a silicon dioxide support is found to be about 600 W m⁻¹ K⁻¹ near room temperature, which is higher than that of common thin-film electronic materials but lower than that of suspended graphene. The lower κ in supported graphene is attributed to phonon leakage across the graphene-support interface and strong interface scattering of flexural modes, which are significant contributors to κ in suspended graphene. Graphene, first exfoliated from graphite in 2004, has attracted attention for its superior charge mobility and mechanical strength. Other carbon allotropes, including diamond, graphite, and carbon nanotubes, have high thermal conductivity due to strong bonding of light carbon atoms. Graphene is expected to have a much higher thermal conductivity than silicon active layers and copper interconnects in current electronic devices, potentially solving heat dissipation problems in nanoelectronics. Despite extensive research on electronic transport in graphene, thermal transport has been less studied due to experimental challenges. Recent studies have reported room-temperature κ of suspended single-layer graphene (SLG) as high as 3000-5000 W m⁻¹ K⁻¹, exceeding those of diamond and graphite. However, the κ-T relation is not well understood. SLG is usually supported on a dielectric substrate for device applications, and substrate interaction affects thermal transport. The study reports thermal transport measurements on SLG supported on amorphous SiO₂, which is the most common device configuration. Despite phonon-substrate scattering, the room-temperature κ of supported SLG is found to be about 600 W m⁻¹ K⁻¹, significantly higher than common thin-film materials. Using quantum mechanical calculations, the study finds that flexural (ZA) modes contribute significantly to κ in suspended SLG. The measured κ-T relation is explained by the suppression of ZA contribution in supported SLG. The study measures the thermal conductivity of three SLG flakes exfoliated onto SiO₂. The results show that the κ of supported SLG is about 3.4 times lower than the highest reported basal-plane value of pyrolytic graphite. The κ-T curve for supported SLG shows a peak at a much higher temperature than that of PG, indicating that phonon scattering is dominated by substrate interaction and umklapp scattering. Theoretical analysis suggests that the ZA contribution to κ is large in suspended SLG, and the measured κ-T relation can be explained by stronger substrate scattering of ZA phonons than LA and TA phonons. The study also shows that graphene exfoliated on SiO₂ still conducts heat efficiently despite phonon-substrate interaction. However, the substrate effect could be different for few-layer graphene or SLG grown on other substrates. These findings highlight the importance of understanding phonon transport