Tech tells me I cannot have internet + phone on Arris TM822G together?

We bought an Arris TM822G so we don't have to lease a modem/gateway from Comcast. Yesterday they activated my internet on it, but had issues getting the phone to work. The techs managed to fix it by morning, but then the internet didn't work. I called and they sent a tech out to have a look. According to this tech who came we need seperate boxes for the phone and internet. Why wouldn't the Comcast techs on the phone tell me that right away? This doesn't seem right to me and if the modem has both phone and internet support it should be able to work. I think the tech just never worked with a modem that supports both. So I am stuck with two seperate boxes for now.

If any Comcast employees want to have a look, these are the ticket numbers:

CR411295563

CR411142120