With endpoint manager, you just have to setup the mac addresses manually, set the tftp or http provision allow in the firewall.
You will have to do something on the phones the first time to point Bremer to your server for the provisioning, but afterwards, they will have the info always short of being defaulted again.
Users will have to power cycle phones to force a reprovision or you will have to remote log in and force the reprovisin if changes were made and are needed instantly. But honestly after initial setup, that is generally rare.
I have a system hosted on Vultr, and I manually created the CFG files for my Yealink phones. I uploaded them to the /tftpboot folder and then in the responsive firewall, I set https provision to other, tftp to reject and http to reject.
I put the remote site IP in the network section as other. I set the. Port assignment in system admin to have https provisioning on default 1443.
I logged into the Yealink phone directly and went to the provisioning tab and told it the URL: https://pbx.domain.com:1433.
Rebooted the phone and it pulled the config.
The newer model Yealink phones come with a one touch service. I have not played with that yet. But I assume those are like the Sangoma phones. You log into the portal and tell it where to find the provisioning server there.
Basically you always have to have some initial method of telling a new device how to find the provisioning server the first time.
You could do DHCP option, all kinds of things.