Can I obtain any free skins for Phobos?
Solution 1:
No, not all Phobos skins are store purchases.
Yes, some skins can be purchased in-game from blacksmiths using drachmae, including a Unicorn skin. One skin is unlocked by defeating the Level 50 mercenary, Exekias the Legend.
The skins that are available in the Helix shop can also be unlocked using Orichalcum Ore. You cannot specify what to purchase with Orichalcum, however, as your reward will be completely random.