To install PHP 7.2, first add repository with command
add-apt-repository ppa:ondrej/php
Now run apt update
apt update
Install PHP 7.2 with command
apt install php7.2
To install additional modules, run
apt install php7.2-bcmath php7.2-bz2 php7.2-cgi php7.2-cli php7.2-common php7.2-curl php7.2-dba php7.2-dev php7.2-enchant php7.2-fpm php7.2-gd php7.2-gmp php7.2-imap php7.2-intl php7.2-json php7.2-mbstring php7.2-mysql php7.2-opcache php7.2-pgsql php7.2-pspell php7.2-readline php7.2-soap php7.2-sqlite3 php7.2-sybase php7.2-tidy php7.2-xml php7.2-xmlrpc php7.2-zip php7.2-xsl