Contact Comcast tech support.
Do you have sufficient DHCP slots to add another device? (They can look up your line and see.)
Are you certain that you're using the right password?
Are you certain that you're trying to connect to YOUR router, not to a neighbor's router that's using the same name as yours?
"Forget" that connection (in your phone), then try connecting again.
If you have a router that allows you to push a button to make it "findable" (I have no idea what Comcast uses), and your phone has an option like that (it's usually called WPS), try using that - push the button on the router, then tell the phone to connect via WPS.
If you get someone good at Comcast tech support, your phone will be on wifi in a couple of minutes.
