Way 1: Sync iPhoto Photos from a Mac to your iPhone using iTunes
In fact, iTunes allows you to do so. However, you can't preview them before transferring. You can choose a better way. If you insist on trying this way, see the steps.
Step 1: Open iTunes and connect your device.
Step 2: Click the "Device" button in the upper right corner. (If viewing the iTunes Store, click the "Library" button in the upper-right corner first.) If you don't see your device, choose Hide Sidebar from the View menu.
Step 3: Click the "Photos" tab. Select "Sync Photos from". Choose iPhoto as the application you want to sync photos from in the pop up menu. Choose to sync all photos or selected photos.
Step 4: Click "Apply".
Way 2: Transfer Photos from iPhoto to iPhone on Mac
Tenorshare iPhone Care Pro for Mac includes a more convenient iOS file management tool to transfer photos and other files like music, contacts, videos from Mac to iPhone and from iPhone to Mac. You can preview files before transferring, which help you to finish the task more convenient and more accurately. Here's how to use it to transfer iPhoto photos from Mac to iPhone.
Step 1: Connect your iPhone with your Mac via a USB cable. And click "Trust" when "Trust this computer" message pops up in your device.