It's more practical at this point to start weaning off carrying a phone at all times. Not necessarily going off grid into the woods, just not carrying it unless you'll need it for something specific that day. I'm not sure more tech is going to solve this issue, we're just digging the hole deeper.
The special thing about mm wave antenna arrays is that you don't need to have a phone on you to be identified by the unique fingerprint of your gait. There's enough information density in that spectrum to resolve your identity accurately even if you're not carrying a phone. And there are papers demonstrating how to do just that.
Just noting that some of those articles are about mm wave devices explicitly designed as radars. But if you dig through you'll find articles geared towards "mm wave antenna arrays", which is a basically a keyword for 5G radio hardware.
