Upconversion luminescence properties from the emissions of Stark sublevels of Er³⁺ were investigated in Er³⁺-Yb³⁺-Mo⁶⁺-codoped TiO₂ phosphors in this study. According to the energy levels split from Er³⁺, green and red emissions from the transitions of four coupled energy levels, ²H_11/2(I)/²H_11/2(II), ⁴S_3/2(I)/⁴S_3/2(II), ⁴F_9/2(I)/⁴F_9/2(II), and ²H_11/2(I) + ²H_11/2(II)/⁴S_3/2(I) + ⁴S_3/2(II), were observed under 976 nm laser diode excitation. By utilizing the fluorescence intensity ratio (FIR) technique, temperature-dependent upconversion emissions from these four coupled energy levels were analyzed at length. The optical temperature-sensing behaviors of sensing sensitivity, measurement error, and operating temperature for the four coupled energy levels are discussed, all of which are closely related to the energy gap of the coupled energy levels, FIR value, and luminescence intensity. Experimental results suggest that Er³⁺-Yb³⁺-Mo⁶⁺-codoped TiO₂ phosphor with four pairs of energy levels coupled by Stark sublevels provides a new and effective route to realize multiple optical temperature-sensing through a wide range of temperatures in an independent system.