Diablo 3 PS4 Drowned Temple issue
At the end of the temple after clearing it, you're supposed to find the 2nd sword fragment of the stranger (exactly where you're standing on your screenshot).
After taking it, you're supposed to bring it back to Deckard Cain in New Tristram.
Here's a site that lets you check every step of The Broken Blade quest.
If there wasn't the sword fragment in Drowned Temple or that there isn't an ongoing event when back to New Tristram, it seems that your game is bugged.
In this case, you should try to stop and launch again the game.