I have just installed PHP 7.3.8 on our server:

> /var/www/html# which php
#=> /usr/bin/php

> php -v
#=> PHP 7.3.8-1+ubuntu18.04.1+deb.sury+1 (cli) (built: Aug  7 2019 09:52:12) ( NTS )...

I've restarted the server and logged in and out of WP. However, WP is still running PHP 7.2.

How do I ensure WP runs on the latest PHP version?