Symptoms

After the upgrade PHPMyAdmin does not load, it requires PHP 5.2+ (the error displayed in the browser).

Cause

PHPMyAdmin works under server (is not moved to any virtual host), so it inherits default server configuration.

Resolution

Only one PHP version can run as Apache module, either 4 or 5, in this case it's PHP4:
# cat /hsphere/local/config/httpd/httpd.conf.startup
LIBPHP4=yes
…
…
LIBPHP5=no
…
…
The solution here will be to switch the server to php_libphp5 and restart Apache.

Please note: if the server is used as Web server and PHP4 is required by some of the scripts, the workaround here will be to create separate virtual host for PHPMyAdmin, specify DocumentRoot as /hsphere/shared/apache/htdocs/phpMyAdmin and make it work as cgi/fastcgi.