PHP navigator doesn't not show inherited members like methods from parent classes. This functionality is available for Java.
This is a major issue as PHP code is more and more object-oriented. For example, Druapl official documentation discourages the use of NetBeans: "Note that NetBeans is missing an option to display the inherited methods and properties from parent Classes and Interfaces which makes it very hard to use for developing code for Drupal 8 and using another editor/IDE is recommended". See https://www.drupal.org/docs/develop/development-tools/development-tools-overview#s-integrated-development-environments-ides (Netbeans section).
This bug was declared in the former bugtracker system and is 11 years old: https://bz.apache.org/netbeans/show_bug.cgi?id=143879