Can I transfer photos from my iMac to my iPhone?

Sure -> Sync photos between your Mac and iPhone or iPad - Apple Support

I have never used iCloud photo. I sync my photos between my 2018 Mac Mini, 2015 MacBook Pro, and my iPhone and iPads and Nikon DSLR using the built in tools in MacOS. And I store them all in my master Photo library on the Mac, and back it up to external hard drives.

I find it very easy to transfer photos and videos between the iPhone and iPads, and the DSLR, and a Mac.

Yes, as I said. Read the directions in that blue url link I posted in the first line In the post above. That blue link is the support document that explains how to sync Photos between a Mac and an iPhone.

You’re very welcome. And it’s really easy to do, but if you experience any issues, just post back and folks here can help. I’ve been sync’ing my photos with my various Macs and iPhones since 2008 without issues.