The large part of the ferromagnetic anisotropy of CoxFe3-xO4 attributed to the presence of Co2+ is explained, for small x, by means of a one-ion model. The residual orbital angular momentum α(~=1) of Co2+ is constrained by the crystal electric field to lie parallel to the axis of trigonal symmetry. Spin-orbit energy λL.S couples the spin to this axis, accounting for the anisotropy energy. By fitting the theory to cubic anisotropy data one finds αλ=-132 cm-1. The assumption that cations are mobile at higher temperatures leads to a quantitative explanation of the annealing-induced anisotropy energy. The mean orbital magnetic moment μL of Co2+ is predicted to be large (μL~=0.5 Bohr magneton) and anisotropic (∆μL~=0.1 Bohr magneton) at low temperatures.