Sophix is a sub-transformation of Believix. It is the power to magically unite with nature and is the first gift of the Gifts of Destiny. It stands for wisdom. It is a source of emotional and instinctive energy which merges with the Believix powers to reach the absolute harmony with nature.
When Diana, the Major Fairy of Nature, decides to take part in the Great Revenge of the Earth Fairies, the Ethereal Fairies give them the Gifts of Destiny because Believix powers are useless against Major Fairies. The Winx used the Sophix powers to bring Diana's forest back to life after the humans harmed it, and to restore the Source of the Forest's magic.
It is unknown if this makes Flora more powerful considering the fact she is already the fairy of nature but since the Sophix causes the Fairies to be in complete harmony with Nature is a whole it may make Flora become in complete harmony with all the Nature around her, not just the plants.
Bloom: Inner Flame
Stella: Drop of Light
Flora: Breath of Nature
Musa: Pure Harmony
Tecna: Superior Order
Aisha: Vital Beat
Sophix comes from the word "sophia" (Σοφία) which is the Greek feminine word for Wisdom. The Sophix is the Gift of Wisdom.