Here are some possible translations depending on the context:
General:
* Pahina ng pamagat (literally "title page") - This is a common translation for the flyleaf, especially if it contains the title and author's name.
* Pahina ng simula (literally "starting page") - This is a general term for the first page of a book, which could be a flyleaf.
* Pahina ng panimula (literally "introduction page") - This is a more specific term if the flyleaf contains an introduction or preface.
Specific:
* Pahina ng pagpapakilala (literally "introduction page") - This is a good translation if the flyleaf is used to introduce the book or its author.
* Pahina ng pahintulot (literally "permission page") - This is a good translation if the flyleaf contains copyright information or permissions.
* Pahina ng pag-aalay (literally "dedication page") - This is a good translation if the flyleaf contains a dedication.
The best translation for "flyleaf" will depend on the specific context and what the flyleaf contains. You can also use a combination of terms to describe it more accurately.