Yes, Flaming Sphere does require concentration. According to the spell description in Dungeons and Dragons 5e:'Duration: Concentration, up to 1 minute'This means that while you are concentrating on the Flaming Sphere spell, you can't concentrate on another spell simultaneously. If you lose concentration (due to taking damage, casting another concentration spell, etc.), the spell ends, and the flaming sphere disappears. So, maintaining concentration is crucial to keeping the sphere active and dealing damage over time.