Smartphones generally don't contain multiple directional microphones that give them the ability to pick individual voices out in a noisy room. They also don't

Smartphones generally don't contain multiple directional microphones that give them the ability to pick individual voices out in a noisy room. They also don't have the advantage of being plugged directly into a wall 24/7, and so any audio surveillance being done would have to take battery life into account, as well as put consideration into the possibility of the device heating up and tipping the surveillance target off that something strange was going on. Further, despite being generally pretty locked down to the average consumer, smartphones are far less of a black box than the echo/home/etc. Both are a concern, but technically skilled users are at least able to take steps to reduce the potential for their phones to spy on them. The only way to reduce any spying potential with the echo/home/etc, is not to have one at all.