Aficionados of the lovely, old-school style of animation on display in the Academy Award-nominated 2010 feature “A Cat in Paris” will be pleased to discover a new hand-drawn tale of adventure from the French filmmakers Jean-Loup Felicioli and Alain Gagnol. Set in a mythical version of New York City — midway between the colorful Gotham of comic books and the rotten Big Apple of film noir — “Phantom Boy” tells the story of a sick child named Leo.