I lost my phone, but my photos were all updated on PhotoStream beforehand. Can I ever retrieve my photos? I have logged onto iCloud and my updated notes from that day are saved but there is absolutely nothing about PhotoStream when I log on. A friend told me maybe I need to log in on an iPhone or iPad, and then my photos will show up. Is this true?
You can't see/ access you fotos directly with the website.
If you did a backup of you stolen iPhone with iTunes or with iCloud and this back up is actual, all is save and with a new iPhone you can choose the backup to be used and all will be like it was on your token iPhone.
Or you take any iPhone, iPad , Mac with iPhoto (can be also your friends one... ) and change the iCloud account to yours than the fotostreams will be downloaded to the device.
In this case you have 30 days because apple stores the fotos only 30 days in the cloud.