If an itinerary involves a destination outside of North America and you hold any OneWorld Sapphire or OneWorld Emerald status you can enjoy OneWorld lounges at any airports along the way even if you hold status on American or Alaskan. It doesn't matter if some of the sectors are domestic, so long as your begin or end your trip outside of North America you get access the whole way through. The restrictions when it comes to lounge access for American and Alaskan only applies if the itinerary is strictly within North America (interestingly OneWorld Sapphire and Emerald members from other programs can enjoy all OneWorld lounges when travelling domestically in the US, it is just AA and AS that apply this punitive measure).

For Philadelphia, there are a couple of lounges you can visit with your ticket. Yes, there are a couple of American Airlines Admirals clubs but I think you'll likely be disappointed with the quality of food there. Provided your AA flight down to LAX departs later in the afternoon one potentially good option is the British Airways lounge (which opens at 3:15 PM) which is located at the A Concourse post security. In terms of LAX lounges to visit, remember you can access any OneWorld business lounge with that ticket, so yes you can visit the Flagship lounge at LAX (located near gate 40 in terminal 4, which is surprisingly good) but also lounges in other terminals like the Qantas lounges in the International terminal. At LAX most terminals are connected together airside meaning if you want to visit the international terminal from the terminal 4 (where AA is) you just need to take a little walk to that terminal. If you hold OneWorld Emerald status through American (i.e. Executive Platinum as your status suggests) you can also enjoy the excellent Qantas First class lounge which has sit down a-la carte dining. That lounge is located in the international terminal on level 5 (follow signs for lounges and you'll see an escalator that you'll take up).

As always, I must provide the usual disclaimer to pace yourself when it comes to lounges and ensure you don't overindulge or miss your flight (remember some of these lounges may require a bit of a hike to your gate).

-RooFlyer88