What is Grim Grin doing in here? Also
Intruder Alarm seems to be useless too. You don't have anything to combo with either of them.
Perhaps try some tutors instead to add some consistency to the deck, like
Demonic Tutor or
Scheming Symmetry (and then mill your opponent's top card).
You seem to have a little bit of zombie synergy going on here, but not enough to make it a zombie deck, and it weakens the mill aspect of it to the point that it isn't great at that either. You are trying to do zombies and mill. You need to pick one. I'd recommend mill since Phenax is the commander, but it is up to you.
Assuming we are doing the mill thing, here are my suggestions.
Get rid of every zombie and everything zombie related.
Now if you are casting things like
mind grind, I would recommend a strategy like this:
1) Ramp. As much of it as possible.
X will need to be around 30 since most players run around 35 lands in there. Your best bet for this would probably be running a lot of black cards like
Crypt Ghast,
Cabal Coffers, Nirkana Reverent and such. Combine them with
Urborg, Tomb of Yawgmoth for as much ramp as possible. Also consider cards like
Bubbling Muck. Now I realize getting 30+ mana will still be difficult, so also think about cards like
Mirari or
Mirrorpool. These cards copy the value of
X when a spell is on the stack (well all copy spells do), so you really only need
x=15ish and then copy it to do it twice. I'd also add in tutors and counterspells to make sure you get the cards you need and you have protection, but that is the gameplan, and a solid one for mill, I think, but mill is meh in general in commander.
Another idea, since the last one doesn't really use Phenax is to build a wall tribal deck, a bunch of creatures with big butts.
I'll leave a few links:
Wall Theme EDHRECScryfall all Blue and Black WallsPhenax EDHRECI think I would go a route with
Tree of Perdition, and try and copy it with spells like
Phantasmal Image,
Rite of Replication,
Stolen Identity, etc. And then I would use their ability to exchange life total of an opponent with its toughness. This would allow you to mill for 40ish at a time when tapping them to use Phenax's ability. Again, tutors and counterspells for consistency and protection.
You know, I've actually won several games by milling. I use Persistent Petitoners. Here is my deck list:
https://deckstats.net/decks/69736/1255436-persistent-pertitioners-edh/en#show__spoilerThe commander I use is
Damia, Sage of Stone, not Muldrotha. My hand was being emptied too fast so I added a simple fix in Damia. Paradox Engined has been banned and I haven't updated the list. What I did was pull out
Paradox Engine, put Muldrotha in the 99 and make Damia the Commander (she isn't in the original deck list, she replaced
Paradox Engine).