We report on the use of photonic resonances in Raman spectroscopy on single nanowires for the enhancement of forbidden modes and the study of the interaction of phonons with free-carriers. This is achieved by suspending nanowire over a trench and detecting Raman scattered light with light polarized along the radial direction. Thanks to the photonic nature of the light-nanowire interaction, light polarization inside the nanowire is modified. This results in the excitation of LO modes, forbidden on {1 1 0} surfaces. We apply this new configuration to the measurement of carrier concentration on doped GaAs nanowires. These results open new perspectives for the study of the interaction of free-carriers or plasmons with optical phonons in nanostructures.