Made profile on Google+? If not, Get invited here
Now like Android Phone, you can upload photos from your Apple iPhone to Google+, by using a ad-ware app named Piconhand, it can be downloaded free from App Store.
Once you have download and installed the add, here's an quick guide how to upload picture from iPhone to Google+
Sign in with your Google details into Google+, on Albums page, you will see your existing albums on Google+
Make sure that your Location Services are turned on
How to find Location Services..Services > Location Services > Scroll to Piconhand
Then create a new album, name it whatever you want, and Circles with whom you will share it.
You can select picture from the library or take a new one for instant upload, according to your app settings.
Finally when you hit the Start button to upload, you will see the progress bar for the current uploading photo, after setting its permissions and all other things, you will be able to see those pictures online.
It is not an Native app published by Apple, until Apple publish its own app for Google+, this app is great to use and enjoy the benefits for Google+ Photos.