PHP Error log level control: htaccess vs php.ini vs code and virtualhost

My recommendation would be to use an httpd environment variable.

This can act as a flag to inform your web application about the environment. Say you had a white label product, there it can be useful for example in setting what configuration should be used with a specific vhost.

<VirtualHost *:80>
  DocumentRoot "/srv/www/foo/public"
  ServerName foo.com

  <Directory /srv/www/foo/public>

    # production | development | staging
    SetEnv APPLICATION_ENV development
    ...

And then in your PHP code you would access it like:

<?php
define('APPLICATION_ENV_LOCAL', 'local');
define('APPLICATION_ENV_DEVELOPMENT', 'development');
define('APPLICATION_ENV_STAGING', 'staging');
define('APPLICATION_ENV_PRODUCTION', 'production');

$app_env = (getenv('APPLICATION_ENV')) ? getenv('APPLICATION_ENV') : false;
if (empty($app_env) || ! in_array($app_env, array(APPLICATION_ENV_LOCAL, APPLICATION_ENV_DEVELOPMENT, APPLICATION_ENV_STAGING, APPLICATION_ENV_PRODUCTION))) {
    throw new Exception("APPLICATION ENV IS NOT SPECIFIED OR IS INVALID.");
}

What I'd do is have totally separate config / INI type files that I include based on the environment. Those could determine error reporting behavior, maintain distinct database connections, anything else dependent on the application environment.