Remote connection to the phone file system

I've studied how it is possible to access the file system of a phone using something like phone number, IMEI number or other identification number of the same way that I can SSH or FTP in a computer if I have its IP address. I've found various Cisco resources such as https://community.cisco.com/t5/collaboration-voice-and-video/ip-phone-sccp-amp-sip-phone-registration-process-with- cucm / ta-p / 3109183 and https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/8_5_1/ccmsys/accm-851-cm/a08procl.pdf

But I was wondering if anyone knew the specific answer to that question. I know that it is possible to remotely access the file system and the operating system of a phone with the help of a protocol.