Sorry for delay in replying. As mentioned, I'm disabled in a way that means I'm only intermittently up to dealing with stuff, and even then only for brief periods.
The good news is that I now have CC on my new phone working with Calibre on the W10 laptop, both as a wireless device and connecting to the content server.
The not quite so good news is that I'm still not absolutely sure what the problem was, or exactly what I did that fixed it (or why it fixed it), and am therefore not entirely confident the problem won't reoccur or that I'll be able to fix it again if it does.
I have been sure the problem wasn't CC, and while pinging both ways, network traffic monitors on laptop and phone, and the other successful uses of other servers on the laptop with other devices on the network, including other apps on the same phone, etc, ruled out many things, my deciding to power up my old Windows 7 laptop that hasn't been on since last June when I got the new Windows 10 one, and finding that CC on my new phone immediately successfully connected to the Calibre (3.20 as nothing on the old laptop has been updated since last June) on the old laptop ruled out many more. It also gave me the chance to check that all my security settings in Comodo on the new laptop were still the same as they were on the old one (where i never had any trouble connecting CC on my old phone to Calibre on the old PC, and now CC on the new phone was connecting to it), and they were (not surprising as when I got the new computer I just saved Comodo's settings from the old one and imported them into Comodo on the new one).
And the only indication of where the problem was and what might have fixed it makes absolutely no sense on three grounds.
Still - everything's working now, and has been for a few days, so I'll leave it at that and hope it continues.