The phase control of the absorption of three photons from the fundamental laser mode and one photon from its third harmonic is studied allowing for a small difference between frequency of the third harmonic and the triple frequency of the fundamental wave. The effect of triple wave detuning upon the (omega(1), omega(3)) absorption is illustrated numerically for model molecule NH3. It is shown that in experiments the phase control can be affected by such a frequency detuning. Several experimental schemes are discussed in order to check out and to confirm this effect. (c) 2005 Elsevier B.V. All rights reserved.