First check that your devices, Lumia phone and Lumia 2520 Tablet, are connected to the same Wi-Fi network. Then check that your device Extras+Info setting is v3.4 or above. If your Extras+Info setting is not up to date, please download the latest version. You can also initiate pairing by doing an NFC tap when the tablet and phone are in the same Wi-Fi network.
Transfer activity from phone to tablet utilizes 3 components, Lumia Storyteller on the tablet, Lumia Share and Extras+Info (settings app) on the phone. Ideally, all of these components should be updated to the current release.