Constant IMAP issues

I have comcast email set up on my iPhone ( with all correct UN , passwords , ports, etc) and I'm constantly having connection issues with IMAP server. It work for a while and all emails come/go and then it stops for few days, i.e. no emails can be sent/received on the phone. 3rd party app is enabled in my account. On the computer it all works fine. Xfinity suggested to use Xfinity app , but that app is not very user friendly and makes opening attachments difficult. Pls help, can not work like that!