Aside from coins.ph you can also try rebit.ph but if you are going to buy huge amount like millions of pesos worth of Bitcoin, I don't think you can do that in just one transaction because they set a limit on how much customers can buy each day, also note that these two exchange requires verification of your identity because of KYC and AML. Try localbitcoins to see if there is anyone with the amount you desire available. Which country are you from? and why do you want to buy Bitcoin here in the Philippines, are you trying to do arbitrage here?