Install PHP 7.3 on Linux

Install Apache 2 server

sudo apt install apache2

Install MySQL Server

sudo apt install mysql-server

Change Mysql root password

mysql -u root
#mysql>
SET PASSWORD FOR 'root'@'localhost' = PASSWORD('yourpassword');

Install PHP 7.3 on Debian

1. Update system

sudo apt update
sudo apt upgrade -y

2. Add PHP 7.3 PPA repository

sudo apt install lsb-release apt-transport-https ca-certificates
sudo apt install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt update

3: Install PHP 7.3 on Debian Linux

sudo apt update
sudo apt install php7.3

4. Install Apache Module for PHP

sudo apt install libapache2-mod-php7.3

5. Install PHP 7.3 Extensions

sudo apt install php7.3-<entension-name>

Example 1.
sudo apt install php7.3-cli php7.3-fpm php7.3-json php7.3-pdo php7.3-mysql php7.3-zip php7.3-gd  php7.3-mbstring php7.3-curl php7.3-xml php7.3-bcmath php7.3-json

Example 2.
sudo apt install php7.3-cgi php7.3-cli php7.3-curl php7.3-imap php7.3-gd php7.3-mysql php7.3-pgsql php7.3-sqlite3 php7.3-mbstring php7.3-json php7.3-bz2 php7.3-xmlrpc php7.3-gmp php7.3-xsl php7.3-soap php7.3-xml php7.3-zip php7.3-dba

Check version installed

php -v

Confirm one

apt policy php7.3-cli

Reset apache server

sudo /etc/init.d/apache2 restart

Notes:

You can update mysql server data from 5.x to 7/8 using 'mysql_upgrade'