S Health was able to see my Garmin Vector power meter. It didn't do much with it, by this was a very long time ago. (I was using it for steps too, last job gave us a bonus for getting a lot of them.)

Your phone shouldn't need to have maps or even a data connection. It should just record your position (48, -122) regularly and then Strava knows how to plot those on a map.

I use a Garmin watch not an app, so that's as specific as I can be.

I've heard good things about Ride With GPS as a recording app, but I've never tried it.