When he's not at work for a while would Chris ever let his hair grow smidge longer, would he grow a stubble? Or would he remain as clean shaven as ever?
The primary reason he’s clean-cut and clean-shaven all the time is that Chris is, as the poets say, a workaholic. He’s very rarely not working.
However - I said this either in a previous headcanon or a conversation with @mccoymostly (or both) - Chris has two settings: workworkwork or lazy fucker. When he’s not working, he has no impulse to do anything but eat, sleep, and become one with his sofa. (Y’know that scene from “Friends” where Phoebe’s hitting the remote and nothing’s happening and someone says “you need to pick it up” and she just says, “eh, forget it”? That’s totally Chris on a day off.)
So, as a natural consequence of that, his hair and stubble grow, because who wants to get up and get a haircut/shave?
It does things to Phil, seeing him like that.