Q: how to copy photos from mac to iphone6

There are several methods including:

via USB cable and iTunes: Sync photos from your computer to your iOS device using iTunes - Apple Support

via iCloud Photo Library (Note that all of your photos from both devices will then be on both devices): https://support.apple.com/en-us/HT204264

via 3rd party service such as Dropbox

via Photo Stream: My Photo Stream FAQ - Apple Support

via 3rd party apps such as https://photosync-app.com/