I found on my system, if having upgraded to php7.3 and phpinfo.php is still showing php7.2, you may need o run the following;
Disable php7.2
sudo a2dismod php7.2
Enable php7.3
sudo a2enmod php7.3
Restart Apache for all changes to take effect
sudo systemctl restart apache2
This worked for me on Ubuntu 18.04.4 and may help someone else.
Darren