In the present report we describe block copolymer micelles based on either poly(dimethylsiloxane-block-ethylene glycol), PDMS₁₅-b-PEG₁₁₀, or poly(ε-caprolactone-block-ethylene glycol), PCL₄₅-b-PEG₁₁₀, loaded by the near-infrared (NIR) phosphorescent iridium(III) complex (Ir1) of [(N^C)₂Ir(N^N)]⁺ type, where N^C is cyclometalating 6-(benzo[b]thiophen-2-yl)phenanthridine ligand and N^N is a bidentate diimine (1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)methyl benzoate) ligand. We also compare both types of phosphorescent micelles (Ir1@PDMS₁₅-b-PEG₁₁₀ and Ir1@PCL₄₅-b-PEG₁₁₀) with aggregate-free non-covalent adducts of Ir1 with human serum albumin (Ir1@HSA). Finally, we evaluate the applicability of all these phosphorescent nanoparticles for oxygen sensing by phosphorescence lifetime imaging (PLIM). Both studied block copolymer micelles are compact (hydrodynamic radii less than 20 nm) and solubilize Ir1 up to at least 8 wt.% with almost 100% loading efficiency while preserving the complex phosphorescence. In contrary, the loading efficiency of Ir1 in Ir1@HSA does not exceed 27% resulting in highest possible loading of 0.35 wt.% and much lower luminescence intensity. Lifetime measurements revealed that Ir1@PCL₄₅-b-PEG₁₁₀ micelles are the best in protecting Ir1 from interactions with the components of physiological media while Ir1@PDMS₁₅-b-PEG₁₁₀ demonstrates the highest lifetime response towards oxygen variations (τ_deg/τ_aer = 2.5), the fastest internalization into Chinese hamster ovary (CHO-K1) cell monolayers, and the strongest intracellular PLIM signal. Though neither system showed ideal combination of desired properties, the present study clearly demonstrates high potential of phosphorescent block copolymer micelles in PLIM oxygen sensing.