No relation to ChaosD1...as far as we know.
Phelous D1 is an evil version of Phelous.
Phelous D1 first appeared in his review of Ghost Ship, where he reveals himself to have been dead all along (as usual) when he reveals a circular tatoo on his hand while proclaiming that he was to harvest souls for the "D1".
He reappears at the end of the following review of Dawn of the Living Dead wearing a trench coat and hat. He only gets a few minutes to proclaim himself as Phelous' new nemesis before purple lightning defeats him.
Since then, he has had one small cameo, and has been referenced a fair amount of times. However, he would not have another significant appearence until many episodes later...
Phelous goes back in time to when he reviewed the film adaptation of Silent Hill. Afterwards, he encounters himself from the past, who has been running from Silent Hill's otherworld at the time. Phelous eventually throws aglaophotis at his past counterpart in a manner similar to Dr. Kaufman in the original Silent Hill game. As Phelous tries to go back in time, his past counterpart reveals the circular tattoo on his hand.
D1 would show up once again right after Phelous regenerates into the Second Phelous (or "New Phelous" take your pick, played by Tomas Guinan). D1 shows up because Phelous made fun of his favorite game, The Magic of Scheherazade, or more specifically, the fact that neither of them could pronounce the title. They bicker about D1 still being of this world for a while before D1 just shoots Phelous in the chest with a shotgun, ending the Second Phelous' run after only 9 minutes. However, during Phelous' next regeneration, D1 is caught in it, resulting in D1 being merged with Phelous, and the latter going back to his old self as a result.
D1 would later make a comeback after Phelous was turned back from a cat by a garlic sandwich (don't ask), only for Phelous to shoot him a few seconds later. However, D1 manages to regenerate, himself through another dead Phelous, only for Obscurus Lupa to use the sandwich to turn him into a cat seconds later.
In the Satan Claus review, it's revealed D1 came back from being turned into a cat thanks to "wibbilty wobbily timey whimey" but a couple reviews later was turned back into a cat in order to make sense of Phelous' "continuity" then accidently killed offscreen. He somehow came back to life to appear in Phelous' april fools day 2013 review of Marvel Comics' "Book of the Dead", but was blown up uncerimoniously by Linkara shortly after revealing himself. From there, he lay dormant until the Dr. Jekyll and Mr. Hyde review, where he appeared briefly as an evil mirror ghost to play Mr. Hyde, though he was rejected by Phelous in favor of the Mortal Kombat character Scorpion.