Problem with typing column vector

Question

\documentclass[a4paper, 12pt]{article}

\usepackage{amsmath,latexsym, amssymb}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[frenchb]{babel}
\usepackage{times}

\begin{document}

On différentie l'égalité: $f(a,b) = f(x,y) = f(x, \phi (x))$ par rapport à $x$:
 \begin{align}
    df_{(x, \phi x)} & \circ \begin{bmatrix}
           \text{Id}_X \\
           d\phi_x
         \end{bmatrix} = 0 
\Leftrightarrow \big( df_{(x,\phi(x))|X},df_{(x,\phi(x))|Y} \big) \circ \begin{bmatrix}
               \text{Id}_X \\
               d\phi_x
             \end{bmatrix} = 0
     \end{align}

\end{document}

I got this output:

Why is there "(1)" at the end of the line even though it didn't appear in the code? How to get rid of it?