Based on his Strava data, Philip was/is a legitimate local trail runner. I haven't checked any races he did, but in the few runs preceding his disappearance, he broke a respectable segment record and was top 10 on a couple of others.
The thing I still don't understand is why he chose what would have been about a 90 min round trip drive for an 8 mile run, leaving behind a network of better trails near him and temperatures that were 30 degrees cooler in Berkeley. I'm curious if he said anything to his wife about why he chose that particular park- heat training? Change of scenery? He could easily have run into Tilden or Wildcat Canyon or any of the other large parks that were closer to him.
I'm not familiar with the trails at the park they're searching, but based on the description of their search for him it would seem that if he's still in the park, he must have become disoriented after suffering heat exhaustion or stroke and wandered more than 100m off the trail in search of water or shade/shelter. If he tucked under something to try and stay cool (ie, he's out of plain sight) and it's far enough away from the main trails they searched, he likely won't be found for a while. It seems safe to assume at this point that he went a good distance away from whatever trail he was initially planning to run on, and is probably a ways off from any trail at all. Assuming he's still in the park.
Pretty heartbreaking if he's still somewhere out in that park, and heartbreaking for other reasons if he's not. Wishing him and his family well despite the long odds.