I think being locked in a 4x4 cell would be a breaking point for most goons.
I thought they showed Phil’s escalating anger throughout the movie pretty well. He was a goon who followed Arno’s orders, but was becoming increasingly upset with Howard’s repeated displays of disrespect. Arno gave Howard a lot more leeway than he would any other debtor because he was family (by law) and Phil lost respect for Arno with each pass. Phil went from pleading with Arno to let him teach Howard a lesson to roughing him up uncommanded on the street to finally just popping him at the end. I think Phil lost all respect for Arno when he just walked away after Howard refused to call ol girl to call off the bet. He went from hanging Howard the window to just walking away like a sad puppy.
Still, Phil was just gonna leave with them. Howard is a complete dumbass for holding them captive. Ol girl already had a huge head start. They couldn’t stop her from making the bet. All he had to do was tell her to go to a hotel off site and wait it out. Could’ve devised a plan to collect with more privacy to allude any goons (Arno may’ve called off the goons with the bet won anyways). But disrespecting a goon so thoroughly like that meant all bets were off