Darius is just flat out rather flexible on works on him with regards to runes and summoner spells. Darius' runes/summoner spells tend to shift over time.
Phase Rush and Ghost both individually work good on Darius, although it's a game of trade-offs where you have to consider what you give up for that extra run down potential.
Without Teleport, you give up lane agency and map pressure/presence. Without Ignite you (potentially) have less kill secure potential (arguably made up by more sticking power but what if they duck under a tower or get close to the safety of an ally and an ignite will secure it but getting another skill/auto in means a tower hit or getting too close to their team that may kill you or make it risky?). Ignite works well with the passive (and offers a touch of grievous wounds) too so it's a question of doubling down on what he already has or just working with less to get more of something else. Ghost doesn't give tenacity just move speed so it only offers some potential sticking power.
Darius has options with summoners though; I've seen pretty much all combinations of those four (flash, ghost, ignite, teleport) even ones where Flash was dropped. Teleport/Ignite and Teleport/Ghost might be the only combinations I haven't seen.
Phase rush means no Conqueror (which is traditionally very good on Darius overall), which means you're skipping out on some healing potential from not being able to go Precision plus Domination tree, for example (Conqueror with stacks + Last Stand + Taste of Blood + Ravenous hunter with a Q can heal for a lot when your opponent thinks you're finished).
I haven't played normal SR games in forever though so I don't know what Darius is having to deal with/doing these days (heard jungling on him was a potential thing?). Right now looking at u.gg/champion.gg seems he's most commonly running Flash/Ghost and sticking with Conqueror but dropping Domination for Sorcery secondary and using Nimbus Cloak/Celerity to add to Ghost to sort of get the benefit of a lot of sticking power Phase Rush would give without dropping Conqueror (although far greater downtime). Not sure if this is jungle or lane Darius running it but seems getting to/sticking to a target is his biggest priority at the moment.
