It could be Perry the Platypus, in a really unexpected turn. Maybe Perry has to keep some secrets from Phineas for his spy work, and one day those secrets are revealed in a way that makes Phin feel betrayed. This would definitely make him mad.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of various fanfictions, and there's a good chance you'll find some for Miles and Phin there.
One popular type could be adventure - themed ones where Miles and Phin go on an exciting journey together. Maybe they are exploring a mysterious new land or trying to solve a puzzling mystery.
The literature forum was a social science forum. Humanities and social sciences referred to the study of human culture, human behavior, human thinking, and other subjects, including literature, philosophy, history, politics, psychology, and so on. The literature forum discussed topics related to human literature such as novels, poems, plays, essays, and so on. It also usually involved topics such as literary criticism, literary research, and literary history.
Maybe Phin gets mad because Ferb keeps taking over their projects without much consultation. Ferb is often very methodical and might start changing things in their grand plans, which makes Phin frustrated.
I can't provide information about the resource forum or the movie forum because this information may change over time and I don't think it's beneficial to provide this information.
However, I can recommend some websites that provide a large number of novel and movie resources. You can search for the content you are interested in on these websites.
Qidian Chinese Network
2 Zongheng Chinese Network
Yuewen Group
Xiaoxiang Academy
5 Feilu novel network
These websites are all well-known novel websites that provide a large number of novel resources. You can search for content that you are interested in on these websites.
In addition, if you like to watch movies, you can find useful information in the following movie forums:
Blue Shadow Forum
2 Douban Movies
3. On the forum of the imdbb
4 Cat Eye Movies
These forums provide a lot of movie information and ratings. You can search for movie resources that you are interested in on these forums.
I hope this information is helpful to you.
One possible plot could be that Phin gets dysentery right in the middle of planning one of their big summer projects. This forces Ferb to take over the leadership role while also trying to nurse Phin back to health. The other kids might be confused at first about what's wrong with Phin, but then they all pitch in to help.