ZyXEL EMG2926 / SIP Voip phone

Hi ! 
My supervisor gave me an Cisco IP Phone to be able to call me at my home. Since my ISP changed my router for a EMG2926 the phone can't register anymore. Before, the phone was creating a SSL VPN easilly and connected to the CUCM at my job. Is there any parameters to change? When I plug the phone directly into another router or into the modem, the connection works.

Thanks!

#CPE_Feb_2019