I've been working at this company for a while and been lucky enough to have really great clients. However, I've recently just been put on a project with a client who is a complete nightmare. I do my best and bend over backwards to make him happy, but he's… A lot. He's asked for my number now (I have a work phone), but I don't want him having even more access to me, stressing me out and damaging my mental health. So I'm setting a boundary and saying no. I'm very responsive on email and slack and we have a ooh service to deal with out of hours calls.
Knowing him, he'll immediately escalate to my bosses. Do I have valid grounds with which to say no? I'm at the point where I feel physically ill when I have to deal with him and I don't need him calling me in my safe space (I work from home).