How to transfer photo from iMac with Sonoma to iPhone?

See the following for information about syncing photos from a Mac to an iPhone: Sync photos between your Mac and iPhone, iPad, or iPod touch - Apple Support

Note that you should leave the original on the Mac. If you delete them from the Mac they will be deleted from the phone the next time you sync. That and other information is included in the "Remove automatically synced photos from your device" section of the above support article.

iCloud Photos is another option to consider. It will sync all photos with iCloud and with both your Mac and iPhone. See: Set up and use iCloud Photos - Apple Support

If neither of the above is what you want, another option is a 3rd party app such as https://www.photosync-app.com/home or https://imazing.com/