Here's a list of guides for Spirit Island that should be helpful. If you find guides on this or other sites that are good, post a link in the comments, I will check it out and likely add it to the list.
Spirits Guides:
pktt's guide to Serpent SLumbering beneath the Island
Phantaskippy's Guide to Phantasms:
Part 1: River Surges in Sunlight
Part 2: Vital Strength of the Earth
Part 3: Lightning's Swift Strike
Part 4: Shadows Flicker Like Flames
Part 5: Thunderspeaker
Part 6: A Spread of Rampant Green
Part 7: Bringer of Dreams and Nightmares
Part 8: Ocean's Hungry Grasp
Part 9: Keeper of the Forbidden Wilds
Other guides: