\documentclass[tikz]{standalone}

\usepackage{pgfplots}

\definecolor{ice1}{RGB}{8,48,107}
\definecolor{ice2}{RGB}{8,81,156}
\definecolor{liq1}{RGB}{33,113,181}
\definecolor{liq2}{RGB}{66,146,198}
\definecolor{int1}{RGB}{107,174,214}
\definecolor{int2}{RGB}{158,202,225}
\definecolor{vap1}{RGB}{198,219,239}
\definecolor{vap2}{RGB}{236,231,242}
\definecolor{vac1}{RGB}{247,251,255}
\definecolor{vac2}{RGB}{255,255,255}

\begin{document}
	\begin{tikzpicture}
	
		\fill[vap1] (0,0) to[out=20, in=230] (3,2) to[out=15, in=240] (9,6) -- (10,8) -- (11,8) -- (11,0) -- cycle;
		\fill[liq2] (3,2) to[out=15, in=240] (9,6) -- (10,8) -- (1.5,8) to[out=275, in=115] (3,2);
		\fill[ice2] (0,0) to[out=20, in=230] (3,2) to[out=115, in=275] (1.5,8) -- (0,8) -- cycle;
		
		\draw[thick] (0,0) to[out=20, in=230] (3,2);
		\draw[ultra thick] (3,2) to[out=15, in=240] (9,6);
		\draw[thick] (3,2) to[out=115, in=275] (1.5,8);
		
		\draw[dashed,thick] (9,6) -- (9,0) node[below] {$T_{c}$};
		\draw[dashed,thick] (9,6) -- (0,6) node[left] {$P_{c}$};
		
		\draw[->,thick] (0,0) -- (11.4,0) node [right] {$T$};
		\draw[->,thick] (0,0) -- (0,8.3) node [left] {$P$};
		
		\draw (7,1.5) node {vapor};
		\draw (5,4.5) node {liquid};
		\draw (1,2.5) node {solid};
		
		\begin{scope}
		\clip (0,0) rectangle (11,8);
		\begin{scope}[shift={(9,6)}]
		\begin{axis}[
			opacity=70,
            axis equal=true,
            hide axis,     
            domain=15:75,
            domain y=0:1,
            view={0}{90},
            shader=interp,
            colormap={liqvap}{
                color=(vap1)  color=(liq2)
            },
            anchor=origin,
            data cs=polar,
        	]
    		\addplot 3 [surf] {x};
		\end{axis}
		\end{scope}
		\end{scope}
		
		\fill (9,6) circle (0.1);
	
	\end{tikzpicture}
\end{document}