Phones are inherently "unsovereignable" as you cannot become a telephone operator and hook into the telephone network the same as you can become a domain owner and smtp provider. Some people use voip providers that provide real numbers but route them over their voip network, like skype used to do, but that's about it. After all, countries where you can own a sim card anonymously are a rarity nowadays, so it is obvious the system does not want you to be sovereign in any way when it comes to this.