  Charge, spin and lattice degrees of freedom are strongly entangled in iron
superconductors. A neat consequence of this entanglement is the behavior of the
A_{1g} As-phonon resonance in the different polarization symmetries of Raman
spectroscopy when undergoing the magneto-structural transition. In this work we
show that the observed behavior could be a direct consequence of the coupling
of the phonons with the electronic excitations in the anisotropic magnetic
state. We discuss this scenario within a five orbital tight-binding model
coupled to phonons via the dependence of the Slater-Koster parameters on the As
position. We identify two qualitatively different channels of the
electron-phonon interaction: a geometrical one related to the Fe-As-Fe angle
and another one associated with the modification upon As displacement of the
Fe-As energy integrals pdsigma and pdpi. While both mechanisms result in a
finite B_{1g} response, the behavior of the phonon intensity in the A_{1g} and
B_{1g} Raman polarization geometries is qualitatively different when the
coupling is driven by the angle or by the energy integral dependence. We
discuss our results in view of the experimental reports.
