Provides a simple manner to obtain a final portion of a file path with an optional desired number of folder levels.

filenameWithLevels.php

/**
 *  Provides a simple manner to obtain a final portion of a file path
 *  with the desired number of parent folders, if any.
 *
 *  @param string $path
 *  @param int $withFolderLevels = 0
 *  @param string|null $withSeparator = null
 *  @return string
 */
function filename_from_path($path, $withFolderLevels = 0, $withSeparator = null)
{
	if (strrpos($path, '/') !== false) {
		$separator = '/';
	} elseif (strrpos($path, '\\') !== false) {
		$separator = '\\';
	} else {
		return '';
	}
	//
	$path = str_replace(['\\', '/'], DIRECTORY_SEPARATOR, $path);
	//
	if ($withFolderLevels > 0) {
		$levels = explode(DIRECTORY_SEPARATOR, $path);
		$included = [];
		$nth = count($levels) - 1;
		for ($n = $nth - $withFolderLevels; $n <= $nth; ++$n) {
			$included[] = $levels[$n];
		}
		return implode($withSeparator ?? $separator, $included);
	}
	//
	$p = strrpos($path, DIRECTORY_SEPARATOR);
	//
	return substr($path,1+$p);
}



////// testing /////////////////////////////

$filepath = 'c:\your\apache\folder\www\myWebApp\storage\files\invoices\543287423987542357237538823.pdf';

$alpha = getFileName($filepath);  // 543287423987542357237538823.pdf
$bravo = getFileName($filepath, 1); // invoices\543287423987542357237538823.pdf
$charlie = getFileName($filepath, 2); // files\invoices\543287423987542357237538823.pdf
$delta = getFileName($filepath, 2, '/'); // files/invoices/543287423987542357237538823.pdf

echo "\r\n--------------\r\n".print_r(compact('filepath','alpha','bravo','charlie','delta'),true);

// see working example at ---> https://onlinephp.io/c/62684
                                                  

you can test it at:

https://onlinephp.io/c/62684