Connect landline service

I need to connect landline phone to purchased router that doesn't have phone jack

That isn't possible. To use their phone service you need to have a modem with phone jacks. In some markets, you can add a second modem for phone-only use. If that's not possible in your area, you'll need to replace the modem with a compatible model or rent one of their all-in-one gateway devices.

ETA: See the "Voice Telephone enabled" devices on https://www.xfinity.com/support/devices and in the "All Compatible Devices" PDF link near the bottom of that page.

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