The composite index ended down 3.64 points at 2,225.72 after trading between 2,222.02 and 2,235.91.
The broader all-shares index retreated 3.71 points to 1,365.74.
Losers led gainers 71 to 34, with 52 stocks unchanged.
Volume was 11.269 billion shares worth P2.204 billion.
"The geopolitical situation in Iran is pushing up oil and other commodity prices and it is creating inflationary concerns. That may put pressure on the central bank to eventually raise interest rates," said Jose Vistan of AB Capital Securities.
Dealers say the market may continue to head lower in coming sessions with upcoming first-quarter corporate results unlikely to help.
"Earnings in the first quarter are likely to be less robust than usual because of the higher taxes companies have to pay," Vistan said, referring to a law that raised value-added taxes and corporate income taxes in February.
Top-traded Philippine Long Distance Telephone Co. (PLDT) closed down P15 to P1,965 while rival Globe Telecom retreated P5 to P885.
SM Investments fell P5 to P214.
San Miguel A shares closed steady at P60 and San Miguel B shares were unchanged at P79.
Philex Class A shares equity in the nation’s largest mining company that are reserved for Filipinos, fell five centavos, or 1.3 percent, to P3.90, snapping a 36- percent gain five centavos, or 1.3 percent, to P3.95, after climbing yesterday to a record.
Class A shares of Lepanto, the nation’s second-largest mining company by market value, fell one centavo, or 2.4 percent, to 40, snapping a eight-day, 86-percent climb. Its Class B shares fell one centavo, or 2.3 percent, to 42, paring this month’s gain to 56 percent.
Bank of the Philippine Islands, the nation’s largest lender by market value, rose P1, or 1.6 percent, to 62. Metrobank, the biggest by assets, gained 50 centavos, or 1.3 percent, to P39.
The 91-day Treasury bill yield, which banks use to set lending rates, fell in the government’s weekly auction Monday, slipping to 4.600 percent from 4.993 percent at the previous auction on April 3. That was the lowest since May 27, 2002. – AFP