I've had this Globe ONU AN5506-04-FA for several years now. I was able to clone my PLDT ONU, also AN5506-04-FA, physical SN to the Gobe modem. However, it doesn't seem to work with PLDT and obtain an internet connection.
I flashed it with firmware version RP2647 from this site.
http://191.5.112.17:8480/files/Firmware/ONU-FiberHome/04-FA/And now it can connect to PLDT's network, and I have another backup ONU. The beauty is I have admin access and hopefully PLDT doesn't or can't update the firmware to lose the admin access like the original modem.
Upgrading is quite easy. I copied the BIN file to a USB drive formatted to FAT32. Removed any volume name in the drive. I renamed the BIN file to "AN5506_04F1A.bin" as UBoot looks for this file on power up and sees it as a recovery firmware. The firmware image must match the ONU hardware version "WKE2.134.285F1A" for it to be accepted and permanently flashed. Wait for all the LEDs to light up before removing.