Your decision on whether you should keep your savings in pesos or dollars depends on your financial status and goals. This becomes clearer when you make your Statement of Asset and Liabilities (SAL) and Personal Income-Expense Statement (PIES) and write your financial plan.
If your plan requires that you spend in pesos in the future, there seems to be no reason for you to keep dollars for your savings. Aside from this, dollar placements have lower interest rates compared to the Philippine inflation rate. You should always earn a higher rate than the inflation rate to make your money grow. Otherwise, your savings will stay the same or even go down.
Because of this, you will only gain from investing in dollar placements if the Peso-Dollar rate continues to decline at a rate that will more than make up for the low dollar interest rates.
Foreign exchange is a tricky subject. As in any investment, spread your risk. You should not put all your savings in foreign exchange unless perhaps you plan to live abroad. You must be very clear on what you want to achieve every time you invest. Pay close attention to the amount you expect to earn and the period of time you expect to achieve this.