In iOS 14 software Apple introduced a feature that checks if you reuse the same password on multiple website, if any of your passwords that are saved are weak, and checks if any of the websites you have passwords saved for have been potentially compromised and their data leaked.
You can read more about it here https://support.apple.com/pl-pl/guide/security/sec7f0432063/web. This said, making sure your Apple ID is secured by strong unique password and 2 Factor Authentication is always a good thing to do.
As for security of your iPhone, it should be secured as long:
- you use a strong passcode and don’t share with others
- you only use apps coming from trusted source such as App Store
- you don’t use/rely on 3rd party profile configuration coming from unknown sources
- you are not trying to install any system modification, often called as system jailbreak