Echoing a variable inside a function

Use the Settings API. A look at my latest plugin may help you to understand how to register a save function for your fields. Most relevant excerpt:

/**
 * Register custom settings for the fields.
 *
 * @see    save_settings()
 * @see    print_input_field()
 * @return void
 */
public function add_contact_fields()
{
    register_setting(
        'general',
        $this->option_name,
        array ( $this, 'save_settings' )
    );

    foreach ( $this->fields as $type => $desc )
    {
        $handle   = $this->option_name . "_$type";
        $args     = array (
            'label_for' => $handle,
            'type'      => $type
        );
        $callback = array ( $this, 'print_input_field' );

        add_settings_field(
            $handle,
            $desc,
            $callback,
            'general',
            'default',
            $args
        );
    }
}

/**
 * Callback for 'register_setting()'.
 *
 * @see    add_contact_fields()
 * @param  array $settings
 * @return array $settings
 */
public function save_settings( array $settings = array () )
{
    $default  = get_option( $this->option_name );
    $settings = array_map( 'trim', $settings );
    $settings = $this->prepare_mail_save( $settings, $default );
    $settings = $this->prepare_phone_save( $settings );

    return $settings;
}

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