How can I transfer picture from my Nikon Camera to my iPhone?

[selina_555]

You don't HAVE to compress it.

To transfer photos onto your phone, set up a folder on your computer named "iPhone photos".
Now put the photos into that folder, as well as all other photos you want to have on your phone.
Plug in your phone, open iTunes, go to your device, then to photos.
Tell iTunes to synchronize your photos with the iPhone photos folder.

Note: You must make sure to back up any photos you have on your phone first, because once you synchronize with that folder, the others will be gone. In future, just make sure that all your photos that you want on your phone will go into that special folder.