photos app won't show iPhone photos

All software is updated (iTunes, iOS, photos ad iPhone)

Could you please post the version numbers? "Updated" could mean the last version of the currently installed system, not necessarily the most recent system. Are you running macOS 10.13.3 and iOS 11.2.5 and 12.7.3? Are your photos and videos in the new space-saving HEIC/HEVC format (Using HEIF or HEVC media on Apple devices - Apple Support)?

Why don't the photos show up? The 'import selected' and 'import all' are obviously greyed out as it not seeing any photos.

What changed, before the photos stopped to show up in the Import panel?

The four most common reasons are: If iTunes doesn't recognize your iPhone, iPad, or iPod - Apple Support

• The photos have been synced to the iPhone with iTunes. Then it is not possible to download them again from the iPhone using a USB connection, because the photos are not in the camera roll.
• The update to iOS 11 may have enabled iCloud Photo Library on the iPhone and optimize storagewithout you noticing it. Then you cannot download the photos from the device, because the photos may be only in iCloud and not on the iPhone.
• You may need to run iTunes first, so you can confirm on the iPhone that is trusts the Mac. (Photos says unlock iPhone when trying import in Photos and then No Photos show)
• Third-party software on your Mac (firewall, antivirus software) may be blocking the access to the iPhone. uninstall third-party security software

Does any of this apply?

On the iPhone I also went into SETTINGS-PHOTO-KEEP ORIGINALS (it was on automatic)

So you have an iPhone model, that can take photos and videos in the space saving format? Your Mac with macOS 10.13.3 can handle HEIC and HEVC media. You should be able to transfer them in this format.

Is iCloud Photo Library enabled, as Larry suspects? Have you checked, if the iOS 11 update turned it on?

You did not say anything about third-party security software. Your iPhone most not show in the USB Device Tree, like shown here, that would be bad: https://support.apple.com/en-us/HT204095

1. Hold down the Option key, click the Apple menu, and choose System Information or System Report.
2. From the list on the left, select USB.
3. If you see your iPhone, iPad, or iPod under USB Device Tree, uninstall third-party security software. If not, contact Apple Support.

On the iPhone I also went into SETTINGS-PHOTO-KEEP ORIGINALS (it was on automatic)

That (I think as you did not actually give the answer) means you have iCloud Photo Library enabled on your phone

If I guessed correctly then the answer is the second one Léonie posted

The update to iOS 11 may have enabled iCloud Photo Library on the iPhone and optimize storagewithout you noticing it. Then you cannot download the photos from the device, because the photos may be only in iCloud and not on the iPhone.

If iCloud Photo Library is enabled on your Phone then you can not import from it via USB as posted - you either have to use I{CL on both devices or neither

LN