The Friedkin Group, Philadelphia Phillies minority owner Stan Middleman and Symphony Technology Group managing partner William Chisholm are among the groups that remain engaged in bidding for the Boston Celtics, according to multiple people familiar with the process. Those three groups, plus one led by existing Celtics investor Steve Pagliuca, have all participated in management presentations with the NBA team, said the people, who were granted anonymity because the details are private. The next round of bids is due at the end of the week.