\usepackage{ifthen,delarray}
\newcommand{\phonarr}[1]{
  \ifthenelse{\equal{#1}{}}{}{\ensuremath{
    \begin{array}[c][ {l} ]
      #1
    \end{array}
  }}
}

\newcommand{\genmap}[2]{#1\  $\to$\ #2}
\newcommand{\phonmap}[2]{\genmap{\textipa{#1}}{\textipa{#2}}}
\newcommand{\featmap}[2]{\genmap{\phonarr{#1}}{\phonarr{#2}}}

\newcommand{\genrule}[4]{
  \genmap{#1}{#2}\ /\ %
  #3\ $\rule{2em}{0.5pt}$\ #4
}

\newcommand{\phonrule}[4]{\genrule{\textipa{#1}}{\textipa{#2}}{\textipa{#3}}{\textipa{#4}}}
\newcommand{\featrule}[4]{\phonrule{\phonarr{#1}}{\phonarr{#2}}{\phonarr{#3}}{\phonarr{#4}}}

\def\fsyll{\,\rm{syll.}}
\def\fnas{\,\rm{nas.}}
\def\fcons{\,\rm{cons.}}
\def\fcont{\,\rm{cont.}}
\def\fvoc{\,\rm{voice}}
\def\fdrs{\,\rm{dors.}}
\def\flab{\,\rm{lab.}}
\def\fant{\,\rm{ant.}}
\def\fcgltt{\,\rm{constr.\ glott.}}

\def\fhigh{\,\rm{high}}
\def\flow{\,\rm{low}}
\def\fback{\,\rm{back}}
\def\ffront{\,\rm{front}}
\def\ftense{\,\rm{tense}}
\def\fround{\,\rm{round}}
\def\flong{\,\rm{long}}

% create as many of these macros as you need

% usage: \featrule{+\fsyll}{+\fsyll\\+\fnas}{+\fnas}{}
%        \phonrule{/i/}{[\~i]}{[m]}{}
%        \phonmap{/amis/}{[am\~is]}