Alyson Stoner is the voice of Isabella Garcia-Shapiro and Jenny in the series Phineas and Ferb .
`` She currently provides the voice of Isabella Garcia-Shapiro and Jenny ( until Season 4 ) in the Disney Channel animated series Phineas and Ferb and personally came up with Isabella 's catchphrase `` '' Whatcha doin ' ? '' '' . ''
Alyson Stoner