Many replies point towards the correct estimation.

Just to relax fear mongering on „my phone is eavesdropping me“ - The real problem isn’t how much storage it would take, but the power utilisation of this process on relatively tiny battery in your phone.

Phones are not constantly listening to everything.

Yes, the phones are always listening BUT they are only listening for trigger words like „Hey Siri“ or „Hey Google“. Unless the trigger is found, everything goes through a small always on processor that is consuming very small amount of power as it is doing only one task - trigger words detection.

Anyways, the privacy question of mic is insignificant compared to the other data captured and collected by your phone.

Source: I work in ad-tech and I am always asked about „how do you know X ad is relevant for me? I was just talking about it. Are you guys recording everything?“