There is no official Team Fortress 2 mobile app developed by Valve available on the Google Play Store.

developed by Valve for the Google Play Store, the community has found several ways to bring the iconic mercenary shooter to mobile devices. Official Status

• True to PC version with no pay-to-win mechanics
• Cross-progression with Steam (yes, really)
• Optimized well on mid-range devices (60 FPS on Snapdragon 720G)
• Full voice chat & text chat support
• All game modes: Payload, Control Points, CTF, Mann vs. Machine

Team Fortress 2 Mobile Overview