iPhone keeps on rebooting after water damage

Used my iPhone to film underwater in a pool, after an hour the sim stopped working, I immediately turned it off and took it to a repair shop for a cleaning the day after, they cleaned the phone’s internals, which indeed had some water inside. And now the phone restarts after a couple of minutes of use, the video playback is slow to start and it seems like the phone gets much hotter.

What could be the problem? Could the mobo be beyond repair because of the water damage? What can I do? (I’m on vacation in a foreign country)