Q: How can I import photos to my iphone from my Mac?

One method is via iTunes photo sync: Sync photos from your computer to your iOS device using iTunes - Apple Support

Another is via Photo Stream My Photo Stream FAQ - Apple Support

With Yosemite 10.10.3 or later you can use the Photos app on the Mac and iCloud Photo Library: iCloud Photo Library FAQ - Apple Support

Other options include 3rd party apps such as https://photosync-app.com/ and 3rd party cloud services such as Dropbox.