Los Angeles LAX to Philadelphia PHL is $108.10 one way on American Airlines and $116.60 on United Airlines. There are more available low fare dates flying United Airlines with every Tuesday and Wednesday in April to May 11 and some Saturdays. American has same days of week. Delta is $149 each way.
American Airlines Philadelphia PHL – Los Angeles LAX (nonstop flights)
$216.20 round trip Saturday April 9 – Tuesday April 12
United Airlines Los Angeles LAX – Philadelphia PHL (one-stop flights)
$233.20 round trip Tuesday May 3 – Saturday May 7
United base fare = $188 earns 5x Mileage Plus redeemable miles.