Wrapper over SplFileInfo. added getMimeContentType, getMimeType methods. Notice! throws a FIleNotFoundException (you should have this class).

FileInfo.php

<?php

namespace app\helpers;

use app\exceptions\FileNotFoundException;
use SplFileInfo;

/**
 * Class FileInfo
 *
 * Wrapper over SplFileInfo
 */
class FileInfo extends SplFileInfo
{
    /**
     * @throws FileNotFoundException
     */
    public function __construct($filename)
    {
        parent::__construct($filename);

        if (!$this->isFile()) {
            throw new FileNotFoundException($filename . ' не является файлом или не найден');
        }
    }

    public function getMimeContentType()
    {
        return mime_content_type($this->getPathname());
    }

    public function getMimeType()
    {
        $extension = $this->getExtension();
        $mimeType = null;

        if (!empty($extension)) {
            switch ($extension) {
                case 'txt':
                    $mimeType = 'text/plain';
                    break;
                case 'odt':
                    $mimeType = 'application/vnd.oasis.opendocument.text';
                    break;
                case 'doc':
                    $mimeType = 'application/msword';
                    break;
                case 'docx':
                    $mimeType = 'application/vnd.openxmlformats-officedocument.wordprocessingml.document';
                    break;
                case 'jpg':
                case 'jpeg':
                    $mimeType = 'image/jpeg';
                    break;
                case 'png':
                    $mimeType = 'image/png';
                    break;
                case 'pdf':
                    $mimeType = 'application/pdf';
                    break;
                case 'zip':
                    $mimeType = 'application/zip';
                    break;
                case 'xlsx':
                    $mimeType = 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet';
                    break;
                case 'xls':
                    $mimeType = 'application/vnd.ms-excel';
                    break;
                default:
                    break;
            }
        }

        return $mimeType ?: $this->getMimeContentType();
    }
}