Why wouldn't they? Only a deeply stupid world leader would carry their phone with them all the time, or conduct any sort of business on it.

My understanding is that the current crop of politicians is terrified of FOIA requests, and so pushes as much to their phones as possible. You can't FOIA many of the apps on there.

This is a cowardly practice. These officials are either overtly cowards, or they are too stupid to understand that their phones are targets for foreign intelligence agencies.