I have an iphone 7 with iOS version 11.2.5 and connect communicate between my phone and my computer comcast email account.
I cannot find the comcast imap registration page and/or the instructions for making the appropriate changes to my phone to accomplish ease of email use.
Normally you should just be able to add your Comcast account to your iPhone's Mail App by going to:
Settings | Accounts & Passwords | Add Account
then input your Name, Comcast email address, and password.
If you need to tweak the settings: