We propose and explore the families of fully tunable, conditional 2 x 2 frequency-domain beamsplitters that result from sideband coupling in phase modulators. Full tunability is obtained by tailoring the driving voltage feeding the modulators, in a design based on the symmetries of this voltage waveform. The most favorable case in terms of success probability is that of first-sideband coupling, which can be implemented by the use of single-tone phase modulation. The use of this device is illustrated by means of several examples based on the use of a wavelength-routed source of pairs of single-photon frequency-entangled states, showing immediate applications as a means of translating to the frequency-domain quantum-processing protocols based on linear optics. ; Ministerio de Ciencia y Tecnología, Spain TEC2008-02606 ; Ministerio de Ciencia y Tecnología, Spain CONSOLIDER-INGENIO 2010 Project, Quantum Optical Information Technology (QOIT) ; Generalitat Valenciana PROMETEO 2008/092 ; Capmany Francoy, J.; Fernández-Pousa, CR. (2011). Conditional frequency-domain beamsplitters using phase modulators. IEEE Photonics Journal. 3(5):954-967. doi:10.1109/JPHOT.2011.2170158. ; Senia ; 954 ; 967 ; 3 ; 5