Answer
Identity for $\tan \left( \theta +\phi \right)$ is expressed as $\frac{\tan \theta +\tan \phi }{1-\tan \theta \tan \phi }$.
Work Step by Step
From the sum formula of tangents, the tangent of the sum of two angles, say A and B, is expressed as,
$\tan \left( A+B \right)=\frac{\tan A+\tan B}{1-\tan A\tan B}$
Thus, for angles $\theta $ and $\phi $ ,
$\tan \left( \theta +\phi \right)=\frac{\tan \theta +\tan \phi }{1-\tan \theta \tan \phi }$
