Below is a MWE that demonstrates my problem. The problem is how the labels move through each slide. It seems as though they are first right aligned and then become centered for the next slide. How can I have each label centered under the tick mark on every slide so that the diagram doesn't move between slides.
\documentclass{beamer}
\usepackage{pgfplots}
\begin{document}
\begin{frame}{Minimal Example}
\begin{tikzpicture}
\begin{axis}[
font=\tiny,
% enlarge y limits={value=0.2,upper},
% scaled ticks=false,
xticklabels={,
\only<4>{\phantom{$\mu-3\sigma$}} \only<4->{$\mu-3\sigma$},
\only<3>{\phantom{$\mu-2\sigma$}} \only<3->{$\mu-2\sigma$},
\only<2>{\phantom{$\mu-\sigma$}} \only<2->{$\mu-\sigma$},
$\mu$,
\only<2>{\phantom{$\mu+\sigma$}} \only<2->{$\mu+\sigma$},
\only<3>{\phantom{$\mu+2\sigma$}} \only<3->{$\mu+2\sigma$},
\only<4>{\phantom{$\mu+3\sigma$}} \only<4->{$\mu+3\sigma$},
},
yticklabels={,},
]
\addplot[blue] coordinates {(0,0) (0,1) (6,1) (6,0)};
\addplot[red] coordinates {(1,0) (1,2) (5,2) (5,0)};
\addplot[green] coordinates {(2,0) (2,3) (4,3) (4,0)};
\end{axis}
\end{tikzpicture}
\end{frame}
\end{document}
The construction of showing labels between slides I took from this solution.