I looked aroumd and found it:
PAL has a general note in their Conditions of Contract on their website :
H. NO SHOW/NON-USERS FEE - Tickets issued, reissued or revalidated in the Philippines, the booking of which is not cancelled 24 hours prior to the date of departure shall be refunded or revalidated only upon payment of a fee provided under the Carrier's Tariff. The No-show/Non-User's Fee may also apply to tickets issued in other countries depending on the fare rules/conditions of the ticket.

In addition, the fare rules specify the amount, here an example from a domestic flight:
NO SHOW / NON USERS FEE PHP 1000 PER SECTOR INCLUSIVE OF VAT.

Is it legal? Probably not, as PAL can't make a reasonable case that they incur any cost by somebody not flying, quite the opposite! And the fact that they are spelling out "tickets issued in PHL" suggests that they couldn't enforce this for tickets purchased in Europe...
But the CAAP passenger bill of Rights doesn't cover it, so unless somebody takes this to court, there is not much you can do...and I don't expect anybody to don't hat anytime soon....
That's why I said, if you can walk away from the ticket, don't pay. I don't think PAL would take you to court either.
If you still want to change ticket after no-show, you can argue or pay the fee...