Thank you for reply, this is a great news for me !
So, I had to insert the 3CX fqdn in the ip phone configuration like this:
3cx.mydomain.com:5060 ?
Or it's better to use ip address ?
Are you using a supported device or a non supported device? If you are using a supported device you only need to follow the provisioning guide for your model. The settings will be auto applied. https://www.3cx.com/sip-phones/