Right- a cell phone’s no different in concept than a keypad lock or any other biometric device used to regulate access to a door.
They can subpoena the passwords or fingerprints or irises or whatever for a cell phone just like they would for one of those other devices.
And you know that even if they did mandate that cell phone manufacturers use some sort of backdoored encryption method, people would just root the things, and install their own un-backdoored encryption inside it.