How to install PHP on Visual Studio Online Environment?

Question

Any ideas how to get PHP to work on Visual Studio Online - environment (preview) for development and test purposes?

I believe it is Debian 9 based and tried to install it by this method (and many other but all with same result).

In the end it looks like this (no matter if I specify the php version or not, install from .deb file or sources):

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package php is a virtual package provided by:
  php7.3 7.3.11-1~deb10u1 [Not candidate version]
  uwsgi-plugin-php 2.0.17.1+8+0.0.3+b3 [Not candidate version]
  php7.3 7.3.4-2 [Not candidate version]
  php7.0 7.0.33-0+deb9u6 [Not candidate version]
  php7.0 7.0.33-0+deb9u3 [Not candidate version]