With the new Vampire skill Blood Frenzy, which allows you to drain your health in exchange for massive amounts of spell/weapon damage, the Phoenix set just got really interesting on bomber builds:
Phoenix
(2 items) Adds 1096 Maximum Magicka
(3 items) Adds 129 Magicka Recovery
(4 items) Adds 129 Spell Damage
(5 items) When you drop below 25% Health, gain a damage shield that absorbs 25000 damage for 6 seconds and deals 8240 Flame Damage to nearby enemies. This effect can occur once every 1 minute.
Blood Frenzy + Phoenix + Strike from the Shadows (new vampire passive) + a typical bomber setup the rest of the way = a really interesting build. It's really high risk because you are taking yourself down to 25% health, but effective use allows your Phoenix proc to operate as another explosion to go off right before Proxy Det, Soul Tether, and (hopefully) Vicious Death.