gateway and external router

My Comcast gateway is working with my pc, TV and digital phone.

The digital phone is on a base and 2 cordless phones. I also  have 2 phones on land lines.

The secure network I have established via the router in the gateway slows my smartphone to a crawl.

However, if I use data or xfinity which is Comcast Wi- Fi the smartphone is snappy.

Question;

Can I disable the warless in their gateway and put an Ethernet cable in the back of that gateway and use my own router or will this mess up my wireless phones??

I don't think I know enough to handle bridging.

Did you ever get this resolved Peter?

I really apologize for not getting back to you. There was a bigger issue with the laptop which consumed my time. Because things are working well, and because I know what  to do should the time come I have all the notes secured. Thank you all very much for your continued support.

I had not responded -  and neither did anyone else.  I was just feeling bad that you had not gotten a response.

Glad to hear that you believe you are on your way to a solution.