You no longer need the Instagram app in order to upload photos. In an effort to make the app more accessible, Instagram has rolled out the ability to now upload via the mobile site, but with limitations. You can’t upload videos, publish to your stories, slide in anyone’s DM’s or use photo filters as yet. Previously you were only able to see your notifications and newsfeed.
Photo editing is also very limited, as you are only able to zoom in/out and rotate photos. See some screen-caps below.