The Tecno PHANTOM X2 Pro-5G (12/256GB) is likely to be a high-end smartphone with the following potential features:

1. Display: A large and high-resolution display, possibly with an AMOLED or IPS panel.

2. Performance: Powered by a powerful processor, likely from a reputable manufacturer, for smooth multitasking and efficient performance.

3. RAM and Storage: The model you mentioned specifies 12GB of RAM and 256GB of internal storage, offering ample space for apps, media, and files.

4. 5G Connectivity: Support for 5G networks for faster data speeds and improved connectivity.

5. Camera System: A sophisticated camera setup with multiple lenses, possibly featuring high megapixel counts, advanced imaging capabilities, and various shooting modes.

6. Battery: A large battery capacity to ensure all-day usage on a single charge, along with fast charging technology.

7. Operating System: Running on the latest version of Android with Tecno's custom user interface.

8. Build and Design: Premium build materials and a sleek design, possibly with a glass or metal body.

9. Security: Biometric security features such as an in-display fingerprint sensor and facial recognition.

10. Additional Features: Other features may include stereo speakers, water resistance, wireless charging, and various sensors.

Remember to check Tecno Mobile's official sources or trusted reviews for the most accurate and detailed information about the Tecno PHANTOM X2 Pro-5G (12/256GB) smartphone.