LAMPP:让Lampp为xdebug使用正确的php版本

I am trying for days now to get xdebug 2.5.1 running on my elementaryOS machine using php7. Finally, I found that two versions of PHP seem to installed and configured on my computer.

php -v leads to

Cannot load Xdebug - it was already loaded
PHP 7.0.15-0ubuntu0.16.04.4 (cli) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
with Xdebug v2.5.1, Copyright (c) 2002-2017, by Derick Rethans
with Zend OPcache v7.0.15-0ubuntu0.16.04.4, Copyright (c) 1999-2017, 
by Zend Technologies

but running phpinfo() in my LAMPP does not display any occurrence of xdebug. So I assume that lampp is not correctly configured to work with the php version that has xdebug installed.

So what do I have to do?