Från POtC Wiki :
Alone and mortally wounded, Philip drags himself to the nearest pool to get some water to drink and use to try and heal his wounds. As he splashes the water, Syrena returned and appeared in front of him. Reunited and free from Blackbeard and his crew, the two profess their love once more. Syrena then told Philip that she could save him from dying. Philip then begged Syrena for forgiveness for all the trouble he brought to her, as she would never have been captured had it not been for him. Syrena kissed Philip, confirming the legend that a mermaid's kiss prevents drowning by giving him the ability to breathe underwater, and pulls him into the pool. Philip was taken by Syrena as they swim through the pools to freedom. His further fate is unknown.