This is probably easier to do for PHP 7.4, but I wanted PHP 7.3 to make sure everything is compatible with existing code. The code below assumes you are doing this in an interactive shell in a Docker container build for creating binaries for AWS Lambda. Doing this is explained here

First, install the necessary tools to build PHP

$ yum update -y
$ yum install autoconf bison gcc gcc-c++ libcurl-devel libxml2-devel -y

Next, build the SSL version required for PHP 7.3 build

$ curl -sL http://www.openssl.org/source/openssl-1.0.1k.tar.gz | tar -xvz
$ cd openssl-1.0.1k
$ ./config & make & make install

Then download and build PHP 7.3, and configure with all the support for accessing MySQL databases

$ cd ..
$ curl -sL https://github.com/php/php-src/archive/php-7.3.0.tar.gz | tar -xvz
$ cd php-src-php-7.3.0
$ ./buildconf --force
$ /configure --prefix=/home/ec2-user/php-7-bin/ --with-openssl=/usr/local/ssl --with-curl --without-libzip --with-zlib --enable-zip --with-pdo-mysql --with-mysqli=mysqlnd
$ make install

Finally, check that the MySQL modules are there:

$ /home/ec2-user/php-7-bin/bin/php -m