my Eye of Eternal Fire drop rate in Plane of Fire
2/39 Chancellor Traxom
1/35 Criare Sunmane
2/36 Jaxoliz Dawneyes
0/43 Quavonis Firetail
0/12 The Fabled Chancellor Traxom
0/13 The Fabled Criare Sunmane
1/12 The Fabled Jaxoliz Dawneyes
0/14 The Fabled Quavonis Firetail
6/204 = 3%
Eye of Eternal Fire is used in one jewelry recipe to make Molten Ring of Incineration. If you're looking to complete your list of learned Jewelry Making recipes.
The newish Agent of Change expedition to Plane of Fire helps a lot with farming it. Lockout timer for the instance is 6.5 days. Mercs are allowed in.
Due to their unresistable Phoenix Charm, the secret to killing the two phoenixes Jax and Criare is to send in your pet to tank (or solo) the phoenix while staying out of range. The pet doesn't get charmed like you or your merc would.