Phineas and Ferb made an appearance yesterday during the Mickey's Very Merry Christmas Party, along with actress Alyson Stoner. They were taping for the Disney Channel's D365 (I know very little about the Disney Channel anymore, so I'm just typing what I was told!) They were in the Tomorrowland Terrace area. Space Mountain has also started soft openings, but I've not ridden yet.
We also have short video clips of Phineas and Ferb, as well as Alyson Stoner! I was told that there are currently no plans to feature Phineas and Ferb in the parks (hopefully that changes, they'd make a great addition to DHS). Also, we do have video from "A Totally Tomorrowland Christmas"!