Got to settings in your Iphone and scroll down to the tapatalk app and select it and the. Check your photo sharing settings, or also under settings select photos and see if you have allowed sharing with tapatalk there
If you use Tapatalk for other things as well, it might help to delete it and reload it. Check to make sure that both your phone and the app are updated as well. I have been having issues with multiple apps locking up and crashing on me...Apple store says to keep everything updated so that's not an issue.