After the pioneering work of Wilson et al. on aluminophosphates, “Al-P-O” and “Ga-P-O” systems have been extensively studied. Various amines were introduced as templating agents in order to produce opened frameworks with attractive catalytic properties. It was shown that the size and the shape of the amine molecule dictate the geometry of the framework. In this respect, the cesium aluminophosphates and gallophosphates are of interest, due to the large size of the Cs⁺ cation, intermediate between that of amines and smaller alkaline cations. Revisiting the Cs-M^III-P-O systems using hydrothermal and solid-state synthesis, we have synthesized several new compounds, presenting layered or intersecting tunnels structures (CsGa₂(OH)₂[(PO₄)H(PO₄), Cs₂Ga₆(OH)₂(PO₄)₆^.1.55H₂O, or CsAl₃(P₃O₁₀)₂ for instance). Our results concerning the role of cesium on the M^III-P-O framework are presented herein. The structural relationships with the analogous phosphates involving either larger organic or smaller inorganic inserted cations are analysed.