Why can't you use
Horn of Heaven to negate the Special summon of V. Lord or Phoenix. I know that it is a monster effect that brings them back, but if you call Jowgen back from the graveyard in responce to the effect, then the monster would not be special summoned despite the fact that the effect that attempted to special summon the monster resolved successfully.
To this end, I would argue that the effect that Special summons a monster from the graveyard, and the Special summon of that monster itself are two indpendent events (or else Call + Jowgen could not stop a monster from being Special summoned as Jowgen does not acutally negate the special summoning effect.) If this is true, then wouldn't all special summons have to go something like this...
Chain link 1 effect attempts to target a monster that will be special summoned to the field if sucessful...then
Responce chain 1 targeted monster now attempts to be special summoned to the field.