Base on our experience, my baby also have 2 passport, uk ang Phil passport. At first i just show to the airport in Cebu her british passport,and since she was born in Pinas and we stay there until she's 1yr old, they're asking me to pay tax which is 2k plus. then I ask why will she need to pay tax when she's was born in Pinas? so they ask me if she have philippine passport.so I gave it to them.they said, nxt time,show the 2 passport to avoid tax...
Hope that helps!