This post is probably too late to help with this lost phone but in the future the minute you realize the phone is missing call the number. If someone answers offer them the reward.
There are some honest people on this island. My caretaker spotted a phone on the road up north by Beach-n-Kitchen. I took it and when it rang I answered and the person hung up. It took three times for the caller to wait long enough to hear me. I explained the situation, he identified the person he was calling and I told him to have the owner call me and identify the phone. He did, it was a Town Council member who is ever so grateful.