I was flying Alaska domestic PHL->SEA today with OneWorld Emerald status (with Alaska) and was able to get into the PHL BA lounge no problem at 4:15pm. (I had prepared myself for a fight as I am very suspicious of how BA lounges treat their OneWorld partners, but in the end it was pretty smooth.) The lounge is fine, nothing special but it’s gonna be your best choice if you’re flying Alaska. You just have to be ok with walking most of the length of the airport.