Unlike iOS, where Instagram is shown as an icon next to Facebook, Twitter, and LinkedIn, there is a different sharing flow for Instagram on Android.
Step 1: Tap the 'Share' icon on the post you'd like to share to Instagram
Step 2: Tap the icon with 3 dots, then tap 'Share'
Step 3: Tap Instagram 'Feed' (Post) or 'Stories' to share to your Instagram
Editing and Sharing to Instagram Feed
A: You can resize the photo, then tap the right arrow
B: You can choose a filter, then tap 'Next'
C: Write a caption, then tap 'Share'
A: The image post will appear in full size - readjust as necessary.
TIP: If you forget the text that is in the post on PostBeyond, the text will automatically be saved on your clipboard. Click 'paste' and edit the text to fit the instagram Story.
B: Continue editing (selecting filter, etc) & 'Send to' Desired Contacts/Your Story