There are at least two bands with this name:

1) Phantasmagoria was an japanese visual kei band. They are known by many of their fans as "magomago (マゴマゴ)."
Phantasmagoria was officially formed on November 01, 2004.
Kisaki, bassist and leader of Phantasmagoria, is also the Executive of Under Code Production, a Visual Kei indies label located in Osaka, Japan. Previously, he was the Executive of the indies label Matina.

Members:
Vocal: 戮(Riku) (KAWON → HISKAREA(研二) → Phantasmagoria(戮) →Bloodly-clown → ｃｈａｒｉｏｔｓ)

Guitar: Jun (Se'lavy → マーディレイラ～Mar’derayla～(純) → Phantasmagoria(Jun) → ａｔｔｉｃ → JUN&伊織)

Guitar: 伊織(Iori) (Se'lavy → マーディレイラ～Mar’derayla～ → Phantasmagoria → 伊織 → JUN&伊織)

Bass: KISAKI(妃) (Ｓｃａｒｅ Ｃｒｏｗ(roadie) → Levia → LAYBIAL → SHEY≠DE → ＧＡＲＤＥＮ → De＝prive → Stella Maria → 廃人黒薔薇族 → La:Sadie's → ＭＩＲＡＧＥ → Syndrome → Phantasmagoria), also solo wroks/side projects: KISAKI, KISAKI PROJECT, KISAKI PROJECT feat.樹威, 妃＆関西貴族)

Drums: 纏(Matoi) (KAWON → HISKAREA → Phantasmagoria → JILL CHRIST)

Former member(s):
Drums: 熾苑(Shion)(Mist of Rouge → Phantasmagoria) He left on February 01, 2005. Matoi took up support drums and then became an official band member on March 12.

After their oneman at Shibuya AX, February 23, 2007, both Iori and Matoi left the band. On April 5th they returned to the band, but only to play their last lives before disbandment. August 31, Kisaki officially retired from music.
Thus disbanding, Phantasmagoria have reunited for some one-shot lives.

2) The Croatian Gothic Rock band Phantasmagoria led since the mid-80ies by singer Tomi Phantasma. The band are active and play frequently at local venues and international festivals (Wave Gotik Treffen, Metal Camp, etc.). They have played with artists such as Type O Negative, The Mission, Mortiis and In Extremo. Still, they don't have an actual LP, but are found mostly on compilations. Although they mostly play their own songs, they are popular for their covers "Djevojka od bronce" and "Gimme Gimme Gimme".