I have a phone but I very much seldom use it. I prefer the communication through email (which I had already included in my job resume).
Is that okay if I don't include a phone number in my job resume since phone is not the best way to contact me?
Should I include my phone
Even if seldom used and your preference is email, you also have to consider the preference of others. I personally prefer to contact people by phone then in person. (you can't get a good read on a person's personality via email.)
That said, I'd probably just skip past your resume since I get applications by the dozen. Now if you were one of only a few I received I might email you asking for a phone number, but honestly it'll hurt your odds of consideration.
What if I prefer Email?
You can specifically mark email as preferred, but offer the phone as backup. If you REALLY want to only be contacted by email, by all means you can omit it, but it could potentially cost you opportunities with those who do not prefer email.
I'm thinking a little out of the box here, but why not sign up for a Google Voice account or something similar, and list that number on your resume? I see a couple of advantages to this:
This is kind of a "best of both worlds" approach that satisfies RualStorge's concern about omitting the phone number. I have done this in previous job searches and it has worked out very well.
If you decide to do it this way, be sure and put a professional voice mail message on your Google Voice account.