In this paper the extended application range of the standard phase-Doppler anemometer (PDA) to particle diameters below the commonly accepted lower limit of about 5-10 mu m is described. The problems that accompany measurements on smaller particles are small scattering cross-sections and ambiguous relations between the measured phase difference Delta Phi and the particle diameter d. A simple, but flexible optical set-up for the transmitting part of a standard PDA system, and a numerical algorithm, which allows careful data evaluation from ambiguous Delta Phi(d) relations, help to manage these problems. Measurements on aqueous suspensions of micron and sub-micron sized dielectric and metalic monospheres, as well as on polydisperse aerosols, are presented and evaluated by means of the proposed algorithm.