Smoke and Mirrors!
You do not need to crack the encryption or read it in transit - you merely need to know the phone number and use SS7 to gain access to the phone. Once you have access you can just read the messages in plain text as the phone has the keys to decrypt the messages.
All phones are back-doored - if the phone can do it, then they can do it. No amount of encryption, firewalls, permissions, domain blocking etc. will stop this. Your messaging apps, social media, SMS, contacts and photos etc. are all easily viewed remotely. Why exactly do you need to break the encryption in transit?
Sim Toolkit exists even with eSIM’s, and combined with S@T Browser has access to your phone. Compatibility Test Suite can download “updates” to your phone and modify the phone temporarily in order to gain access. The same is true with the Dynamic System Installation Service. Managed Provisioning can remote control the phone. Maybe Opportunistic Network Services could connect your phone with my phone for access, or perhaps a buffer overflow bug in MMS could trigger code execution. Perhaps you use a predictive text service that checks the spelling by sending everything you type to a remote server to be “spell checked”. Or maybe you just use plain old WAP from yester-year which still exists today to modify ring tones on your phone or more likely install apk’s or shell code. Or maybe just push an “update” specifically for your phone over the air. I mean nobody is going to take the digital signal processor, pipe it to netcat going to a server and listen in on the phone, are they? What, even when your not using it? While you’re at it you might use the Easter Egg apk to modify the system permissions and send the print spooler all those supposedly encrypted files to an online “print service”.
This is all smoke and mirrors much like you having to download an app that uses bluetooth to determine whether someone with covid was too close to you for an extended period of time. The phone companies already store all the data with triangulation - there was no need for a covid app, but that would bring too much attention to the data being collected on you every day. How do you think you can make uninterrupted phone calls while travelling - you’re connected to several towers at the same time and the strongest signal is selected. This allows accurate triangulation down to a square metre. See - no covid app was required, just like breaking end to end encryption isn’t required either. All your phones are open books in many, many ways.