I'm trying to register the phone by using this proxy as TLS protocol but it's not working with me
It's not working ... - somewhat vague description of the issue, isn't it ? Turn on syslog&debug messages of VOice application and capture them:
Debug and syslog Messages from the SPA3xx, SPA5xxG, SPA9xx, & WIP310 IP Phones
It will help you/us to identify the issue cause.
As a pure blind shot - proxy in question is using TLS certificate issued by CA you didn't configured as trusted. Secure connection can't be established as a result. Use "Custom CA RULE" configuration option (Provisioning tab) to import CA certificate into trusted certificates store. Remember - it's just blinds shot hint based on "it's not working" description of the issue ...