A hedge fund startup run by Michael Phelps, a former head of European credit at BlackRock Inc., has attracted a $200 million investment from Blackstone Group LP, according to a person with knowledge of the matter. That puts Phelps’s Tresidor Investment Management on course to become one of the largest new funds in London this year. Stuart Roden, a former chairman of Lansdowne Partners, is also backing Tresidor and will join as a non-executive chairman, the person said, asking not to be identified because the information is private. Spokesmen for Blackstone and Tresidor declined to comment.