You must have something Debian8 or OMV 3 in there to want php5. You don't want to see erasmus or jessie anywhere.
Sorry, but i dont really understand your answer.
All i did so far was installing Debian 9 from here: https://www.debian.org/CD/netinst/
After that i followed the instructions you've sent me.
As far as i understand the error, php5 is missing. Is it possible to just install php5? I am really new to linux.
It says Debian 4.9.144-3.1 (2019-02-19) is installed.