This paper reports synthesis of pure and mixed-phase TiO₂ nanoparticles using a sol-gel technique with titanium isopropoxide as a precursor. The prepared samples were then calcined at different temperatures. Variation in calcination temperature has been analyzed on particle size and crystalline phases, morphology, bandgap, and crystallinity using X-Ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray Spectroscopy (SEM-EDX), and UV-Vis spectroscopic analysis, respectively. Moreover, XRD data reveal anatase and rutile phases of TiO₂ depending on the calcination temperature. From this, one may observe that the calcination temperature greatly influences the presence of anatase and rutile phases of TiO₂. It can change the phase from the metastable anatase phase to the stable rutile phase. Also, increasing the calcination temperature can increase the particle size as estimated by the Scherrer equation, which was found to be 7 nm to 60 nm with a temperature from 400 °C to 1200 °C. SEM analysis shows the growth of spherical-shaped nanoclusters with irregular morphology, whereas EDX spectroscopic analysis confirms the purity of the samples. It has been observed that increasing the temperature reduces the bandgap through UV-Vis spectroscopic analysis. The photocatalytic degradation of Phenol Red was studied by using synthesized anatase TiO₂ nanoparticles.