Follow all the steps from https://linuxsecurityblog.com/2016/01/28/install-dvwa-on-ubuntu/
Starting from Ubuntu 16.04 LTS, php5 support is dropped!
Hence, install all php7 as below
apt-get install libapache2-mod-php apt-get install php-mysql apt-get install php-gd
Rest all the commands in the blog works !!
Enjoy Exploiting!
Tidbits! 