caution sign on photos from phone (in iOS macbook)

My mac is using OSX

which version of OS X? 10.10 Yosemite? 10.11 El Capitan? 10.12 Sierra or 10.13 High Sierra?

Only High Sierra can handle the new image and video formats.

Are you importing from your iPhone using a USB connection? Then you can convert the images and videos when downloading from the iPhone.

The iPhone settings should be:

• Settings > Photos. In the "Transfer to Mac or PC" section disable "Keep Originals" to ensure the media being converted when importing.
• For the Camera:

1. go to Settings > Camera.
2. Tap Formats.
3. Tap Most Compatible. This setting is available only on devices that can capture media in HEIF or HEVC format.
4. All new photos and videos will now use JPEG or H.264 format.

You can convert the HEIC images you already imported using the online converter at heictojpg.com

I do not know of any online service to convert the videos. You may want to delete the videos you already imported and to import them again from the iPhone, after you changed the settings on the iPhone.

Or try to figure out, why your Mac cannot handle the upgrade to a newer system. With an iPhone running iOS 11 it is much more convenient to have a Mac running High Sierra.

What kind of cell phone do you have?

How are you transferring the photos from the cell phone to the Mac?

If your cell phone is an iPhone with iOS 11, and if the iPhone is now using the new HEIF format for photos, you need either to change the settings on the iPhone to keep the photos in a more compatible format or to export them to the Mac in a more compatible format, see: Using HEIF or HEVC media on Apple devices - Apple Support

You're welcome 🙂