You can reboot the phone via: 

• Web-interface
• Phone menu
• Provisioning, check-sync

Via the web-interface you can restart the phone.

Go to: Settings - System - Reboot and Reset

From software 2.13 or higher, the reboot option is also available for the user login.

From software 2.13 or higher, the reboot option is also available via the phone menu:

Go to: Settings - Reboot

See: SIP message - provisioning