The Philippine Peso (PHP) amount is calculated based on the BTC amount in your wallet.
Thus, it is normal for the PHP amount of your Balances to change from time to time, since the Peso equivalent changes whenever the price of BTC changes.
What does remain constant is the BTC amount in your wallet. You may check this and other cryptocurrency balances on the Portfolio tab of your account.
If you notice any unexpected changes in the amount of BTC or other cryptocurrency, please go to your Transaction History to review the incoming and outgoing BTC transfers initiated from your wallet.