Phone is connected to Router. Boots up and show no service.
Added the Phone MAC in the Admin Portal and assigned the user
Logged to web portal of the YeaLink T48S Phone with default admin/admin password.
Everything looks fine.
Rebooted the phone few times. Still No help. Phone shows NO SERVICE.
Welcome to the forums. You're talking to other users here. If you want to reach Verizon, you need to call or chat with them.
Your VoIP phone needs to be configured for whatever VoIP service you're using. Since you can login into the phone, that tells me it's connected to the LAN. You need to use the phone's web portal to configure service. Get the credentials from your VoIP service provider.