You have to down-load the photo from the phone to your computer, then via the computer upload to a photo hosting web site. I understand RV.net has a place you can send a photo to and then use the URL of that photo from the hosting site in your post. You cannot post it directly from your computer or your phone. It has to be saved on a world wide server somewhere, unless you have a dedicated computer somewhere that you are using for an internet server yourself.
Edit! Or upload to a photo hosting web site directly from your phone it it is internet capable.