Why is the image not centered for the right node?
\usepackage{tikz}
\usepackage{mwe}
\tikzset{
image/.style={
path picture={
\node at (path picture bounding box.center) {
\includegraphics[width=2cm]{example-image}};}}
}
\begin{document}
\begin{tikzpicture}
\tikzstyle{node}=[rectangle, minimum width=2cm, minimum height=1cm, thick, draw =black!100, node distance = 16mm]
\node[node, image] (y_src_i) [label=below:$\phi_i$] { };
\node[node, image] (x_src_i) [right=of y_src_i, label=below:$\phi_j$] { };
\end{tikzpicture}


right of=y_src_i,. (Just in case you haven't read esdd's comment below. – Aug 26 '18 at 15:17