Taken from
Bureau of Immigration website
DEPARTURE
Filipinos with dual or multiple citizenship, who presented a foreign passport at the time of their admission into the Philippines may be cleared for departure without need of surrendering a certificate, permit or proof of payment of imposable immigration fees, provided, he/she also shows a genuine and valid passport and/or Identification Certificate. However, if the Filipino does not have a Philippine passport, an Emigration Clearance Certificate (ECC) fee of P710.00 shall be charged for using a foreign passport upon departure.
In the arrival, stay and departure of Filipinos with dual or multiple citizenship, where the Filipino presents a Philippine passport and a foreign passport, the arrival or departure stamp shall be stamped on both passports. In the foreign passport, the immigration officer shall put either of the following notations on the provision for the authorized stay in the arrival or departure stamp:
PP- if a Philippine passport is also presented, or
IC if an Identification Certificate is presented.
(MEMORANDUM ORDER NO. AFFJr. 04 025 dated 14 December 2004).
When we left with our son, he only had UK passport, therefore we had to pay the fee.