How do i transfer photos from Mac to iphone

First make sure both devices are signed into the same Apple ID and iCloud Photos is enabled on both, if it is, your photos sync automatically.

If you’re transferring manually, open Finder, connect your iPhone via USB, select your device in the sidebar, go to the Photos tab, and check Sync photos from. Choose your folder or Photos library and click Apply. If Finder doesn’t detect the iPhone, trust the device when prompted and try a different cable or port.

Also ensure your iPhone has enough free storage for the transfer.

Here's how to do it:

Sync your photos manually using the Finder - Apple Support (IE)

Or you can use airdrop:

Use AirDrop to send items to nearby Apple devices - Apple Support (IE)