The phone only needs the GPS data. Strava and other activities apps translate that to maps later. I used an older iPhone for over a year without any phone/data plan, just using GPS. No problems.

You *can* also have a map app on the phone. It's separate from Strava and one has no influence on the other. I usually have two map apps on my iPhone and Android phones: Apple maps with the iPhone; Google maps on the Android phone; maps.me on both. As long as the latest offline map is downloaded it'll work fine offline via GPS.

Strava is occasionally finicky and can lose ride/activity data. And if an activity is accidentally deleted from Strava, either the mobile device app or the browser, it's gone. No way to recover it.

But Wahoo Fitness is free, records the same data as Strava, and can be uploaded to Strava. It only needs GPS to run, same as Strava. Uploading Wahoo Fitness data to Strava creates a separate identical record. You can delete it from Strava without affecting the Wahoo Fitness record, and vice versa -- but I keep both since the data takes up very little room on the phone.

Incidentally, if you use Google maps and enable timeline tracking, your activities will also be recorded to the Google maps timeline by default. That record is private, just between the user and Google. Records can be deleted later. It's a handy backup in case Strava fails. And Google maps timeline can't be falsified or modified, it can only be deleted entirely. So it's a handy backup for legal or documentary purposes. I run it in case something happens and there are no witnesses or I'm unconscious, but it also confirmed my version of events when I was hit by a car this spring. And I've used it once or twice to recreate a Strava log when Strava failed. Google records GPS data more consistently -- so far it's never had a glitch.