Just at a glance, you have some random dimir good-stuff in here, like
mindleech mass. Think about taking those out for cards that focus on your strategy more. Also maybe it's just me, but I think taking out
leyline of the void and
planar void could help a lot and open more possibilities. A lot of these cards I'm suggesting don't work well when the
void effects are out.
More ramp - You need more acceleration, with artifacts like
dimir signet,
arcane signet,
talisman of dominance,
commander's sphere, and other similar effects. This deck won't do squat until you get Phenax out, so this will help.
Charix, the Raging Isle - He's a 4 mana 0/17 my guy. Seems like a good fit.
Command tower - Seems like you missed this commander staple. Cheap land that does everything you need.
Duskmantle guildmage - He can drain your opponents' life very quickly and cheaply.
Keening stone - A fun card that can quickly take someone out of the game if they have enough cards in the graveyard.
Diluvian primordial,
sepulchral primordial - Both of these are very well suited to commander and lend themselves nicely to your strategy.
Things like
wight of precinct six - They will get massive very fast.
Glacial wall is better than several of the walls you have. There are also better walls in the world than the ones you run, just an fyi.
Lazav, Dimir Mastermind - It can take any nice creatures you mill along the way
Guiltfeeder is fun, but might not be great if you play against lots of black decks.
Protection for Phenax! - Cards like
swiftfoot boots,
lightning greaves, and
darksteel plate prevent removal of your commander, as this deck won't do much without him.
Anyways, it was fun to find these cards! Hope you use some!