Q: All old photos disappeared on Photo App on Mac

I am currently travelling and had to delete some old photos on my phone to clear space, but I knew they were already on my laptop (in the photo app).

Are you using iCloud Photo LIbrary? It is a syncing service.

If iCloud Photo Library is enabled, your devices will be in sync.  iCloud will ensure, that you are seeing the same photos on all devices. So, if you delete a photo from your iPhone, it will be removed from the Mac as well.

Disable iCloud Photo Library on your iPhone, if you do not want the same photos on the iPhone as on your Mac.

See:   iCloud Photo Library FAQ - Apple Support

Have you checked the Recently Deleted album?  If you did not yet empty it, you can restore the photos from this album.  Other wise you can restore your photos only from the last backup you made, before you erased the photos from iCloud Photo Library.

If you do not have a backup, try recovery software immediately. Most recovery programs have a free trial mode, so you can see what can be recovered, but you will have to pay to actually restore the files.

• For example File Salvage can restore photos - download here:  http://www.subrosasoft.com/index.php?main_page=product_info&products_id=1
• Or Disk Drill:  (http://www.cleverfiles.com/)

Recovery software is expensive, so compare the results, before you buy it, but don't let the Mac erase and overwrite more files, until you have restored your photos.

I am using iCloud, but I thought that it would save all my photos, on my mac and on the cloud (that system was the backup) so that I could delete them on my phone and continue taking pictures. But now they are deleted everywhere?

That is a common misunderstanding.  iCloud Photo Library and iCloud Drive are no backup.  They are the central storage of your photos and documents and mirrored on all devices that are syncing with them.  Delete a photo anywhere from one of your devices and it will be removed from iCloud and the deletion will sync to all devices to make the photo libraries identical on all devices.  Add a photo on any device to iCloud Photo Library and iit will appear on all devices. 

If you deleted your photos from iCloud Photo Library on your iPhone, they will have been deleted from all photo libraries syncing with iCloud, yes.

I deleted all the pictures in "recently deleted" on my phone - to make sure I had the space for new ones.

 

Does this mean my photos are nowhere to be found? I should download the  restoring system?

Then the photos will be gone completely. If you do not have a current backup on your Time Machine use data recovery on your Mac immediately.  The longer you wait, the more image files will be deleted, that still could be recovered.