First mentioned in Chapter 2066 when Shi Feng accepted the quest from the Tier 5 Archangel Vatra, afterwards he received the item.
He uses the flute in Chapter 2897
Apparently the Dragon Summoning Flute is actually a replica.
[Dragon Summoning Flute (Replica)] (Tool, Legendary Rank Item)
A horn rumored to summon a flock of Dragons.
- Spend 3,000 Advanced Magic Cores to summon five Dragons to assist in battle for 3 hours. Cooldown: 15 days. (The Dragons summoned can only fight NPCs. They cannot fight players or monsters.)