Can I clear my iPhone camera roll without losing any photo?
Some explanations about where your iPhone photos are stored: 


the iPhone Camera Roll
Sure. This is the only standard thing that happens.
the iCloud photo stream
Happens only when you have enabled the My Photo Stream option in Settings-&gt;iCloud-&gt;Photos
iPhoto/Aperture projects
Will be the case if you connect your iPhone to you Mac and sync/export your photos.




Now based on the above, deleting photos from you Camera Roll do the follow in each case:


will simply... delete them from your Camera Roll. They may still be in the Recently Deleted Album of your phone for some days.
will also delete them from your Photo Steam since this is something for sharing, not storing/backing-up. Do not confuse this with the iCloud Photo Library (Beta)
will not affect your photos in the iPhoto projects, since these are not synced automatically or something.




Edit after your explanations:

Deleting a photo from your Camera Roll will also delete it from the Photo Stream. And this applies to all your linked devices.

One should think the Photo Stream as a single common Album that all the devices have access to. Hence, any change to it, is reflected to all devices.



Long story short, if you have your photos saved in your mac you can safely delete them from your iPhone. If you feel uneasy with that, you can simply try it with a couple of photos and make sure that everything worked as you expected