installing php7.3 alongside php7.5 on ubuntu code example
Example 1: install php 7.3 ubuntu
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: ubuntu install php 7
sudo apt-get install php libapache2-mod-php