As well as other devices. I've unplugged my google home, but like many people, I have several devices with cameras and microphones in my house. What can I do to ensure they're not recording or listening to me?
I think the answer here depends on how much trust you have for the different levels of tech in your phone. If you don't trust anything, the answer is install a hardware switch for the microphone or cover it with a sound blocker when you're not talking (just like if you don't trust your laptop's camera, put a piece of tape on it). If you trust the hardware, but not the OS, install something like Lineage to replace stock. If you trust the OS, but not the apps, uninstall any app that might have access to the microphone (especially "bad actor" apps like Facebook) and only use web versions.
If your baseband is pwnd -- and it is to some definition of pwned. The unit can appear off and still be recording.
Citation: The NSA document leaks.
Just a thought, is there a way to capture all out-going traffic from one's phone at least when it's not been used?
You can get SIMs from carriers that allow you to forward the traffic to a VPN server of your choice (often used in enterprise to make mobile devices part of the internal network without a battery-consuming on-device VPN client).
If you’re in the UK a company called Andrews & Arnold (no affiliation besides being a longtime customer & reseller) provides those out of the box with no setup fees and an “okay” price per megabyte of data. Otherwise get in touch with carriers but I think most of them would have a setup fee.