@curiousigor thanks for the question. Since the group run is primarily an audio experience it's hard for a runner to keep track of a lot of other runners without overwhelming amounts of commentary or a really good memory. We experimented with the number and found eight to be a good compromise.
We will roll out mass live runs in the near future. These will combine overall race commentary with comparisons within your own group.
The phone number mechanism is a Branch.io feature so you can send yourself an App Store link if you're on a desktop computer. We don't keep (or even know) the phone numbers involved. However, we agree the vanilla version of that experience isn't a good one so we'll update the page.
Racefully