Not all aspects should have Pheonix Lords. the Pheonix Lords, or Asurya, were the first exarchs, and all pupils of Asurman (with the exception of Asurman). Many Aspects have been created since then, but many fall out of fashion soon. In theory, after long enough an Exarch from a newer shrine could become a Pheonix Lord, but perhaps the other aspects have not been around long enough for this. Alternativly, some Pheonix Lord suits of armour could be stuck on a far off world, or a Pheonix Lord could be stuck in the webway.