There is big security issue with tapatalk. Anyone can read any PM.
I know that phpbb.com does not suport tapatalk but there are many phpbb forums with tapatalk plugin on.
You must have account in phpbb forum with tapatalk.
Next take link to PM on this forum and copy it to mail or chat in tapatalk.
Link like this ucp.php?i=pm&mode=view&p=2105316
On the phone/tablet, run the link in the tapatalk app.
When You change pm id in link (p=....), You can see any PM in this forum.
I made two security tickets on the tapatalka page, at first (I made it on the second of April) I did not even get an answer or ticket number. After second (two weeks later) they asked for additional information, but still they did not even give me a ticket number.
I was tested it in 2 different phpbb forums, in one there was phpbb 3.2.2 and tapatalk plugin 2.0.8 - both newest ones.