As EPEL is not yet ready, you must enable "remi" repository which provides lot of packages usually available in  EPEL

Repository installation :

# dnf install https://rpms.remirepo.net/enterprise/remi-release-8.rpm
# dnf install dnf-utils
# dnf config-manager --set-enabled remi

And, for example, to install PHP 7.3

# dnf module install php:remi-7.3
# php --version
PHP 7.3.5 (cli) (built: Apr 30 2019 08:37:17) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.5, Copyright (c) 1998-2018 Zend Technologies

Notice, if you want to install various version simultaneously, the Software Collections of PHP 5.6, 7.0, 7.1, 7.2 et 7.3 are also available.

# dnf install php56
# module load php56
# php --version
PHP 5.6.40 (cli) (built: Apr 30 2019 11:08:08) 
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies

Time to open a good bottle of Champagne !