https://mapcomplete.org is usable like an app on your smartphone,  even though it's just a website.
If you log in on the website, you can add/edit things on the go.

Depending if you use an iPhone or an Android phone, you can use different apps; 

- https://every-door.app (works on both iOS and Android)
- https://streetcomplete.app is Android only
- http://vespucci.io is Android only
- https://apps.apple.com/app/id592990211 (Go Map!!) is iOS only