How to get Proof of Theorem with package phfthm

I am trying to use the package phfthm to have a proof with the indication Proof of Theorem 1, and the like.

I am almost exactly using the example provided in the package documentation, at page 15, but I only get Proof of 1, without the word Theorem, and cannot understand where I am making a mistake.

Here is my example:

\documentclass[]{article}

\usepackage[resetstyle]{phfthm}

\begin{document}

\section*{Introduction}
This is a theorem
\begin{theorem}[Gauss]
\label{thm:Gauss}
For a closed surface $S$ enclosing a volume $V$, we have
\begin{equation}
\oint_S\vec u\cdot d\vec S = \int_V(\vec\nabla\cdot\vec u)\,dV\ .
\end{equation}
\end{theorem}
Then the proof.
\begin{proof}[*thm:Gauss]
text of proof
\end{proof}

\end{document}


You have to load hyperref to provide \autoref, which is needed to print the type of proof. If \autoref is not available, \ref is used as fallback and thus only the number appears (cf. https://tex.stackexchange.com/a/137433/29873). This could have been stated more clearly in the documentation (there are only rather hidden remarks). Anyway, here we go:

\documentclass[]{article}
\usepackage[resetstyle]{phfthm}
\usepackage{hyperref}
\begin{document}

\section*{Introduction}
This is a theorem
\begin{theorem}[Gauss]
\label{thm:Gauss}
For a closed surface $S$ enclosing a volume $V$, we have
\begin{equation}
\oint_S\vec u\cdot d\vec S = \int_V(\vec\nabla\cdot\vec u)\,dV\ .
\end{equation}
\end{theorem}
Then the proof.
\begin{proof}[*thm:Gauss]
text of proof
\end{proof}

\end{document} 