why can't I edit iphone photos on my mac?

Are the phone photos in HEIC format?

If so, your macOS is to old and doesn't recognise them. You can set your phone to take jpg images by going to camera settings>Formats and selecting "most compatible"

You can edit iPhone photos directly on the iPhone. To edit them on your Mac, connect your iPhone to the Mac and import them into your Photos Library and edit them there.

If you already did the import and can't double click on a photo inside of the Photos program to edit it, there may be something wrong with your Photos Library. Try creating a new one, hold down the option key when starting up Photos and create a new Photos Library, you can call it iPhone Photos or something like that. Then connect your iPhone and import the photos into that new Library. You should be able to edit them there.

If the problem you described is happening with your already existing Library, I still recommend creating this new Library for your iPhone images; you can return to that existing Library by again holding option when starting Photos and selecting that previous Library to open it. Then close Photos, and reopen it following instructions here https://support.apple.com/en-us/HT204967 to try to "repair" it. In case this repair does not work, you should make a second copy of the Library you are trying to repair first.