Uneasy pack: every 150 open guaranteed common or uncommon
Frightening pack: every 100 open guaranteed common - rare
Scary pack: every 75 open guaranteed uncommon or rare
Terrifying pack: every 25 open guaranteed rare
Horrific pack: every 15 open guaranteed rare or ultra rare
Dreadful pack: every 5 open guaranteed ultra rare.
It will also show how many you need to open for a guaranteed from each pack and it resets every time you get a new phobie from that pack