No, normally nobody can view the code.
Think of this .. there are at many sites: config.php
with username + password to database, often MySQL.
If it was not very safe, then we would not put user+pass in such a file.
But there is one case, when by accident it could be possible.
It is if the Web Server start serving .php files as text-files.
In a web server .php is configured to be executed by php.exe
and interpretated as PHP Code.
If by accident this server config (httpd.conf for Apache) was changed
and so .php was displayed, then we should be able to
read config.php with all the goodies!
Good thing is, that this happens almost never.
But there is a very small chance.
So small it doesnt bother many people.
I am not bothered.
🙂