# apt-get install apt-transport-https lsb-release ca-certificates
  # wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg
  # echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" > /etc/apt/sources.list.d/php.list
  # apt-get update

Then use apt-get install to install one of these:
  * php5.6
  * php7.0
  * php7.1
  * php7.2
  * php7.3
  * php7.4