Q: how do i access music on my iMac to my iPhone?

If you are asking how do you move music from your Mac to your iPhone you use iTunes to do this. Apple can explain this best in Move content from iTunes on your computer to your iPhone, iPad, or iPod touch - Apple Support

If you what you mean is playing music that is stored on your Mac from your iPhone, you can do so with HomeSharing.

Use Home Sharing to share iTunes content with other devices - Apple Support

What I do is sync the i-Phone to my i-Mac. You do that with i-Tunes. Then while your phone is still connected to the Mac, you go into the phone settings in i-Tunes and select the playlist you want on your phone Assuming you have playlists created. If not it's easy to do as in rkaufmann87's post), then you re-sync the phone again and all the tunes in that playlist will be on the phone.

Your welcome!

You're welcome. And now you're an accomplished i-Tunes / i-Phone jockey !