There are exceptions though.
As per PhilHealth Circular No. 06, series of 2001, retroactive payments are not allowed except when a member can show proof of sufficient regularity of premium contributions or payment of nine (9) consecutive months or three consecutive quarters within the last 12 months prior to the missed quarter. If you meet this condition, you shall be given a grace period of one month immediately after the missed quarter to pay retroactively including the current calendar quarter.
For newly enrolled members (with less than 12 months reckoned from date of enrollment), retroactive payment for the missed quarter including the current calendar quarter shall also be allowed within the month immediately following the missed period.
This privilege is granted only once every 12 months.
Reference: PhilHealth IPM FAQs.
However, even if you miss a quarterly payment, you may still be eligible to avail of PhilHealth benefits if there is sufficient regularity.
Save yourself the worry and just pay your premiums on time.