unable to sync photos from iMac to iphone

The option to sync 'selected albums' is not available

New iMac with OS X Yosemite 10.10.4

Do you mean, when you are syncing your iPhone with iTunes? Where do you store the Photos library?

Check the following:

• Do you have iCloud Photo Library enabled on your iPhone in the Settings > iCloud > Photos? Then you can no longer sync photos using iTunes at all. Disable this setting on the iPhone, if you are not syncing from your Mac using iCloud Photo Library. Sync photos to your iPhone, iPad, and iPod touch in iTunes - Apple Support
• Is your current Photos Library enabled as the System Photos Library in the Photos Preferences on your Mac? Photos > Preferences > General > Use as System Photo Library? the option should be dimmed to be active.
• Is your Photos Library on a locally mounted volume, that iTunes can access?

If iTunes cannot find the Photos library it helps sometimes to quit both Photos and iTunes and to restart the Mac, to force Photos to write its preferences again and to update the Photos Library.

If that still does not help, your Photos library may have a problem.

• Try if removing the iPod Photo Cache will help as described here: iTunes: Understanding the iPod Photo Cache folder
• Repair the Photos Library. It might have a problem if Photos crashed or you moved it: Repairing is described here: https://help.apple.com/photos/mac/1.0/?lang=en#/pht6be18f93

You're welcome 🙂 Great, that it was the easy fix!