How can utilizing separate folders for different functionalities, such as guestbook and photo album, enhance the organization and readability of PHP code in a website?

Utilizing separate folders for different functionalities, such as a guestbook and photo album, can enhance the organization and readability of PHP code in a website by keeping related files together and reducing clutter in the main directory. This approach makes it easier to locate and maintain specific features, as well as prevent naming conflicts between files.

```php
// Example folder structure:
// - guestbook/
//   - index.php
//   - functions.php
// - photo_album/
//   - index.php
//   - gallery.php
// - includes/
//   - header.php
//   - footer.php
```
In this example, the guestbook functionality is contained within the "guestbook" folder, while the photo album functionality is in the "photo_album" folder. This separation allows for better organization and readability of the code.