We present sensitive Giant Metrewave Radio Telescope (GMRT) and high-resolution Arecibo HI 21-cm observations of the damped Lyman-α absorber (DLA) at z=0.2212 towards OI 363. The spectra are in excellent agreement and yield a spin temperature T_s = 890 ± 160 K, far higher than T_s values measured in local spirals, but similar to values obtained in the majority of DLAs (T_s 1000 K). The high velocity resolution of the Arecibo spectra enables us to obtain estimates of physical conditions in the

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... sorbing clouds by fitting multiple Gaussians to the absorption profile. The spectra are well fit by a three-component model with two narrow and one wide components, with temperatures T_k_1 = 308 ± 24 K, T_k_2 = 180 ± 30 K and T_k_3 = 7600 ± 1250 K, respectively. The last of these is in excellent agreement with the expected temperatures for the WNM (5000 - 8000 K). The mere fact that components are seen with lower temperatures than the estimated T_s implies that the absorber must have a multi-phase medium. We use the measured 21-cm optical depth and the above estimates of the kinetic temperature to obtain the HI column density in the various components. The total column density in the narrow components is found to be (CNM) < 1.9 ± 0.25 × 10^20 cm, while that in the wide component is (WNM) > 1.26 ± 0.49 × 10^21 cm. Thus, the WNM contains at least 75 of the total HI in the z = 0.2212 DLA, unlike our Galaxy, in which the CNM and WNM have equitable contributions; this accounts for the difference in the spin temperatures of the z = 0.2212 system and local spirals, suggesting that the DLA is probably a dwarf or LSB type galaxy (abridged).