User blog comment:Mobo85/An Interview with...Phineas and Ferb's Aliki T. Grafft/@comment-1328700-20110923200827/@comment-406459-20110924041048

Here's your answer direct from Aliki herself: "Yes the show is hand drawn, 2-D animation. I believe there was some CG animation with the robots from P n F Across 2nd Dimension movie"