After pairing, your call sound goes to your home phone through Bluetooth by default. Sometimes you want the call on the cell phone itself instead.

When a call comes in, your cell phone shows a choice of where to send the sound: Bluetooth, which is Cell2Jack, the cell phone, or the speaker. Pick the one you want on the call screen.

On iPhone

You can set the iPhone to always send call sound to the iPhone speaker, and even to answer on its own after a set time. Open Settings, then Accessibility, then Touch, then Call Audio Routing, and choose what you want.

On Android

Use the audio choice on the call screen to send the sound to the phone or speaker instead of Bluetooth.