For what it is worth, I've been using Comcast internet service with VOIP phone service for over seven years. From my experience, a managed switch is probably overkill. The slowest component in your network is the bandwidth allocation from the internet service provider. I haven't had any significant voice quality concerns with my network. I would occasionally get a poor connection, but hanging up and placing the call again would resolve the issue.

Just make sure to use a switch (not a hub) which can handle non-blocking, wire-speed packet switching at a rate of 10 Mbps or higher. Either of those switches you mention would be fine, although I would suggest letting your router handle the QOS management. Do choose a decent router that can handle the peak packet rate and has QOS management features. I haven't needed to enable QOS on mine, but I don't usually max out the upload bandwidth.

Enjoy!