Attaining an extremely efficient photocatalyst has drawn a great deal of attention in the worldwide pursuit of using solar power as an abundant and cheap energy source. Layered compounds have demonstrated a wide range of physicochemical properties that support their potential practical applications. Because dimensionality plays a crucial role in determining fundamental properties of lamellar structure, when they go under exfoliation down to few-layer or monolayer nanosheets, their characteristics will differ from those of their stacked bulks. The photocatalytic properties of these few-layer or mono-layer materials can be improved through in-plane and inter-plane structural modification by doping with metal or non-metal elements. Among the various layered materials, graphitic carbon nitride (g-C3N4) has emerged as one of the most promising photocatalysts due to its metal-free nature, abundance in raw material, thermal and physicochemical stability and suitable bandgap. Although its bulk structure shows a weak photocatalytic activity, its thermally or chemically exfoliated nanosheets demonstrate greatly improved activity. Further, the electronic structure of the nanostructures can be modified by elemental doping with triazine units to activate the π-conjugated system in the photocatalytic reaction. In this review paper, we analyze the latest developments, particularly in the area of phosphorous-doped graphitic carbon nitride (P-doped g–C3N4) photocatalysts and their molecular and structural modifications for improving H2 generation and CO2 conversion to solar fuels. •A brief historical background for g–C3N4 has been presented.•Challenges and perspectives regarding g–C3N4 photocatalysts were discussed.•The latest developments on P-doped g–C3N4 photocatalysts were reviewed.•The modifications for improving H2 generation and CO2 conversion were analyzed.•Prospects regarding P-doped g-C3N4 for photocatalytic applications was mentioned.