The only pesos I take IN to the Phils are the ones I was left with previous trip.
I just change enough at the moneychanger on the way out of the airport building to pay for a taxi to my hotel, and perhaps for the hotel first night, then change some more (£s) at a moneychanger near the hotel, next day. Better rate than the airport, and certainly MUCH better than anything you'll get in the UK.