How to Post on Instagram From a Clipboard on the iPhoneby Charlotte Mission
Your iPhone’s clipboard allows you to copy and paste text on your phone with just a few taps. Although you can't use the clipboard feature to copy and paste images, you can post captions, descriptions and tags on photos via the Instagram app or the Web page. The copy and paste process on an iPhone is similar to the one you use on a computer, but there a few differences to accommodate the touchscreen technology.
Tap and hold the text you want to post on Instagram and select "Copy" from the menu that appears.
Go to Instagram and initiate a new post. Upload a photo and click the “Next” button.
Tap and hold your finger in the caption text box to bring up the context menu. Click “Paste” to place the text.
Tap “Done” to post the image and text.