There isn't much in English. So unless you read French, your best hope is The Government of Philip Augustus (U Calif, 1991) by John Baldwin. Baldwin was responsible for a huge transcription and publishing project of Philip's materials in the 1970s out of which came this book. Despite the title it's not a book about government - it's about Philip and the development of Capetian power during his life. It's the standard reference for Anglo and non-Anglo scholars while being high readable.