I don’t think there is a single refactoring available for this out of the box, but there are a number of tools to automate it in steps.

Use “Inline” refactoring to eliminate the direct parent:: calls.

(I hoped that Structural Search would be able to identify the relevant calls, but trying it out locally I could only get a list of classes, not the lines where the call happens. It’s possible I just didn’t get the right settings.)

Move the properties and methods using the “pull members up” and “push members down” refactorings:

1. Place the cursor in class B
2. Choose Refactor -> Push Members Down
3. Tick all properties methods
4. Click “Refactor”

Note that if there is more than one child class of B, this will create copies of the methods in all of them. Alternatively, you can use “Pull Members Up” to move them to class A.

Since you selected all properties and methods, class B will now be empty.

Use structural find and replace to make all classes inheriting from B inherit from A instead:

1. Open the “Replace structurally…” dialog
2. Select the built-in template under PHP -> General -> Class that extends another
3. Edit the “Search template” to class $a$ extends \Full\NsName\B {}
4. Edit the “Replace template” to class $a$ extends \Full\NsName\A {}
5. Click “Find”
6. Review the results and click “Replace Selected” or “Replace All” if you’re happy

Use Find Usages to find any other references to class B, and replace with A or C as required.

Finally, use Safe Delete to have PhpStorm perform one last check for usages before deleting the class completely.