The low-temperature magnetic phase diagram of the multiferroic system FeTe2O5Br down to 300 mK and up to 9 T is presented. Short-range magnetic correlations within the crystal layers start to develop already at similar to 50 K, i.e., far above T-N1 similar to 11.0 K, where the system undergoes a magnetic phase transition into the high-temperature incommensurate (HT-ICM) phase. Only 0.5 K lower, at T-N2, the system undergoes a second phase transition into the low-temperature incommensurately modulated (LT-ICM) phase accompanied by a spontaneous electric polarization. When the magnetic field is applied, the transition temperatures shift depending on the field orientation. In the case of B parallel to b and B > 4.5 T, the HT-ICM phase disappears along with the electric polarization in the LT-ICM phase. The field dependence of the magnetic transition temperatures is explained in the context of the magnetic susceptibility behavior. Similarities and differences between the novel well-established magnetoelectrics are discussed.