Stones was a regular starter before he had his dodgy period where he had a torrid time with injuries and issues in his personal life.
It looked like he had one foot out the door, but that's not because he wasn't good enough - he had shown a world class level already and won multiple titles with Pep at that point.
There isn't a comparison in this squad to the situation that Phillips has found himself in - Rodri, Grealish, Stones, Ake etc all had difficult bedding in periods, but they all still got their chances and when they had shaky performances, Pep persisted with them.
Phillips has just been in the abyss from the outset. His case isn't like any before him. I think the fundamental problem is that Pep simply doesn't rate him, but Phillips simply is happy sitting tight as you say.
Completely detriment to his career at this stage in my opinion and if he does stay beyond this window, will be gone on loan in January after his situation won't have changed (bar a truly terrible injury crisis) and his place in the England squad is under threat (I think it probably already is).
Unfortunately the pressure is going to continue to build for him with each game he doesn't get a look in - this isn't a situation where he doesn't play and fans forget about him. We're seeing Rodri being run into the ground and our £45m back up sit on the bench smiling week after week despite not getting a minute of football. His omission is going to be a major talking point every game and if he does get an opportunity and doesn't peform, the reaction will be tribal.