\documentclass{article}
\usepackage{ifthen}
\usepackage{epsfig}
\usepackage[utf8]{inputenc}
\usepackage{newunicodechar}
  \newunicodechar{⁻}{${}^{-}$}% Superscript minus
  \newunicodechar{²}{${}^{2}$}% Superscript two
  \newunicodechar{³}{${}^{3}$}% Superscript three

\pagestyle{empty}
\begin{document}
$|\nabla \phi|^2 = 1$
\pagebreak

$\nabla f\nabla \phi = 0$
\pagebreak

$|\nabla \phi|^2 = 1 $
\pagebreak

\end{document}
