Purpose: This study evaluated the usefulness of using a single annulus phantom for daily quality assurance (DQA) of two PET/CT systems with different specifications and axial field-of-view (AFOV) lengths. Because of differences in AFOV, system-specific ⁶⁸Ge annulus phantoms of different sizes have conventionally been used for each scanner. Materials and Methods A 55 M㏃ ⁶⁸Ge annulus phantom (Eckert & Ziegler Isotope Products, Germany) was used for both the Discovery MI and OMNI Legend PET/CT systems (GE Healthcare, USA). Based on the manufacturer’s recommended DQA program, PET detector status was monitored over 60 working days before and after the transition in phantom use and evaluated using visual inspection and parameter reports. For image analysis, the NEMA IEC Body phantom was prepared with a 10:1 sphere-to-background activity ratio according to the EARL recommendation. Images were reconstructed using Q.clear+TOF+PSF, Q.clear+OSEM+PSF, TOF+PSF, TOF, OSEM+PSF, and OSEM, in accordance with the institution’s standard torso imaging protocols. Statistical analysis was performed using R. Results: DQA results showed minimal changes in the major parameters: coincidence mean (-0.1%), coincidence variance (0.4%), singles mean (-0.5%), singles variance (-0.3%), block busy mean (3.0%), timing mean (2.1%), and energy shift (-1.1%). Paired t-test results showed no statistically significant differences (P > 0.01). In the NEMA IEC Body phantom analysis, maximum recovery coefficient (RC) values varied from -0.31% to 0.63% compared with individual phantom use, while mean RC values ranged from -0.13% to 0.10%. These differences were also not statistically significant (P > 0.01). Regarding radiation safety, the operator’s annual external exposure was estimated to be 15.124 μ㏜ for phantom handling and 1.089 μ㏜/m during transport. The average annual external radiation exposure was approximately 100 μ㏜ when the total transport distance was 77.94 m. Conclusion: This approach may improve the efficiency of radioactive source management and provide economic benefits by reducing the cost of purchasing multiple sealed sources. These findings suggest that the integrated use of a single annulus phantom is a practical and efficient strategy for quality control in PET/CT systems.