Curly Calligraphic capital A?

The closest I could find is TypoUprightBT:

    \documentclass[12pt]{article}
    \usepackage{amsmath} 
    \usepackage{fontspec}
    \pagestyle{empty}
    \newfontfamily{\uprightcal}{TypoUpright BT}

    \begin{document}%

    \[ \text{\uprightcal{A}}\mkern1mu(\theta, \phi) \]

    \end{document} 

Example of the font


The A of your image might seem the same of full mt2pro package:

enter image description here

\documentclass[12pt]{book} 
\usepackage[mtpccal]{mtpro2}
\begin{document}
\[\mathcal{A}(\theta,\phi)\]
\end{document}

I think the letter has been retouched to get bold with an external program that uses TrueType fonts. In the image you can see that in the character map there is the bold font (MT2MCS):

enter image description here