Petapixel:

The LR/Instagram plugin does exactly what you think it does: it lets you post images to Instagram directly from Lightroom. No need to export and use some third party Web client or get the photo onto your smartphone.

I’ve only just started to use Instagram more seriously. The “need” to post from the iPhone was a real pain. If you use both Instagram and Lightroom, this $10 donationware plugin will really come in handy.