Single doped CaWO4:Er3+ phosphors were synthesized and studied for application of optical thermal sensing within a wide range of 98–773 K. Ratiometric strategy utilizing two luminescence intensity ratios, one between host and Er3+ band (LIR1) and second between different Er3+ transitions (LIR2), results in self-referencing temperature readouts. The presence of two temperature-dependent parameters could improve thermometric characteristics and broaden the working temperature range compared to a usual single-parameter thermometer. Thermometric performances of prepared samples were evaluated in terms of thermal sensitivities, temperature resolution and repeatability. The highest sensitivity of 2.09% K−1@300 K was found for LIR1, whereas LIR2 provided more accurate thermal sensing with a temperature resolution of 0.06–0.1 K. Effect of Er3+ doping concentration on sensing properties were studied. The presented findings indicate that CaWO4:Er3+ phosphors are perspective in dual-mode thermal sensing with high sensitivity and sub-degree resolution.