  Modified Growth with CAMB (MGCAMB) is a patch for the Einstein-Boltzmann
solver CAMB for cosmological tests of gravity. Until now, MGCAMB was limited to
scales well-described by linear perturbation theory. In this work, we extend
the framework with a phenomenological model that can capture nonlinear
corrections in a broad range of modified gravity theories. The extension
employs the publicly available halo model reaction code ReACT, developed for
modeling the nonlinear corrections to cosmological observables in extensions of
the $\Lambda$CDM model. The nonlinear extension makes it possible to use a
wider range of data from large scale structure surveys, without applying a
linear scale cut. We demonstrate that, with the 3$\times$2pt Dark Energy Survey
data, we achieve a stronger constraint on the linear phenomenological functions
$\mu$ and $\Sigma$, after marginalizing over the additional nonlinear parameter
$p_1$, compared to the case without the nonlinear extension and using a linear
cut. The new version of MGCAMB is now forked with CAMB on GitHub allowing for
compatibility with future upgrades.
