Q:

How to use Phonetic Symbols in LaTex

How to use inverted A character(Phonetic Symbol) in an equation in LaTex? Do I have to use any specific package for it? I used \textinvsca, but it says "undefined control sequence"

A:

There are a myriad of ways you can achieve this. Most notably, consult How to look up a symbol or identify a math symbol or character?.
This reveals you need tipa (more specifically, \usepackage{tipx}):

\documentclass{article}
\usepackage{tipx}
\begin{document}
A\textsc{a}\textinvsca\textsc{a}A
\end{document}

You can also rotate-and-scale a regular A:

\documentclass{article}
\usepackage{graphicx}
\newcommand{\textinvsca}{%
  \reflectbox{%
    \rotatebox[origin=c]{180}{%
      \resizebox{!}{.35\baselineskip}{\textsc{A}}}}}
\begin{document}
A\textsc{a}\textinvsca\textsc{a}A
\end{document}

