On a few episodes, Phineas shows an angrier side of himself, first seen in the Phineas and Ferb the Movie: Across the 2nd Dimension movie, where Phineas gets angry at Perry after finding out his secret identity because Perry "never trusted him" by telling him the truth, but later realizes that Perry kept his identity hidden because if Phineas and his family found out, Perry would be forced to relocate to another family.
Pada beberapa episode, Phineas menunjukkan sisi yang lebih marah dari dirinya sendiri, yang pertama kali terlihat di film Phineas and Ferb the Movie: Across the 2nd Dimension, di mana Phineas marah kepada Perry setelah mengetahui identitas rahasianya karena Perry "tidak pernah mempercayainya" dengan memberitahukan dia yang sebenarnya, tapi kemudian menyadari bahwa Perry menyembunyikan jati dirinya karena jika Phineas dan keluarganya tahu, Perry akan dipaksa untuk pindah ke keluarga lain.