Q:

Hphantom of minus sign in math mode

I would like to align the parenthesis in following two equations using \hphantom
\documentclass[varwidth]{standalone}
\begin{document}
\noindent
$d\cdot i\hphantom{j}\qquad\hphantom{-}\;(\ldots)$\\
$d\cdot j\hphantom{i}\qquad-(\ldots)$
\end{document}

I know I could use the align environment. But I was wondering if it is possible to fix this easily by understanding which whitespace is missing.

A:

Use \mathbin{} 
\documentclass[varwidth]{standalone}
\begin{document}
\noindent
$d\cdot i\hphantom{j}\qquad\mathbin{\hphantom{-}}(\ldots)$\\
$d\cdot j\hphantom{i}\qquad-(\ldots)$
\end{document}

https://www.sharelatex.com/learn/Spacing_in_math_mode

For relational operators, such as < , > and =, LaTeX establishes
  \thickmuskip space. But for binary operators such as +, - and x, the
  \medmuskip space is set. The difference is almost unnoticeable.
You can force the spacing used in binary or relational operators, so
  you can define your own.

\begin{align*}
34x^2a \mathbin{\#} 13bc \\
34x^2a \mathrel{\#} 13bc
\end{align*}

The previous example sets a particular spacing before and after # by using \mathrel (relational) and \mathbin (binary) commands.

