Is it possible that if I connect my cell phone via Bluetooth with my laptop it appears like a mp3-player in Banshee so I can sync podcasts easily?
That depends on the brand and model of your phone. If you can treat your phone as a USB Mass Storage Device, then there's a chance Banshee will be able to support it out of the box. If your phone doesn't work, you can always submit a bug report to the Banshee team requesting support for your specific phone. See the Hardware section on Banshee's FAQ page for more information about which devices are currently supported.