most i had on a phone screen was 3 people at once. it also was for a gov clearance level contract gig so maybe that's their thing iono
eventually got the job even though i started fucking up bad on the phone convo once one of the dudes got irrationally mad at me for saying "function" instead of "method" while describing something(java role)

actual interviews vary obs
had anywhere from 2 people 30-40 minute each
to full day of panels (3+ ppl a cycle)
once i had to white board brain teasers for 2 hours straight(didn't get the job)
once i was asked nothing technical or brain teasey at all
u can't call it really. just be prepared