When you say phone app you don't really say which phone, but since I'm of the opinion that the iPhone is the only device worth using and developing for there are several flight log app in the app store today. They are all for actual pilot logs from what I can see, but there are choices ranging from free to rather costly. A few have GPS ability to mark your location when logging. Another option that may work well for you is Bento. A personal database tool. You can customize the fields you need and creating a simple log is very simple and easy to do.