We say that a map
$f$
from a Banach space
$X$
to another Banach space
$Y$
is a phase-isometry if the equality
\[ \{\|f(x)+f(y)\|, \|f(x)-f(y)\|\}=\{\|x+y\|, \|x-y\|\} \]
holds for all
$x,\,y\in X$
. A Banach space
$X$
is said to have the Wigner property if for any Banach space
$Y$
and every surjective phase-isometry
$f : X\rightarrow Y$
, there exists a phase function
$\varepsilon : X \rightarrow \{-1,\,1\}$
such that
$\varepsilon \cdot f$
is a linear isometry. We present some basic properties of phase-isometries between two real Banach spaces. These enable us to show that all finite-dimensional polyhedral Banach spaces and CL-spaces possess the Wigner property.