It's too late in the year for mating, plus one already had an egg-sac, so would not mate. Also, I'd say both spiders are females due to their size.
They're probably eating each other, since P. phalangiodes is a highly cannibalistic species.
Edit: Didn't see the photos properly, she probably dropped her egg-sac since another female coming along is a big threat which she needed to neutralise - she couldn't do that while carrying an egg-sac. Good find, though! I've never seen a spider drop an egg sac.