For actual conversation, the best thing is to combine a structured app (like the Babbel they mentioned) with something more focused on speaking. Speaky works pretty well offline and lets you record audio and send it to native speakers to correct, then you can listen to their corrections. It's not "real-time conversation" like Zoom, but for someone with little time it's practical because you respond whenever you want.
Another thing not many people mention: put English subtitles on when you watch series or YouTube on your phone. It's not really an app as such, but it trains your ear for free and naturally. It's tough at first, but then you start recognizing patterns. Duolingo is way more gamified than practical; it makes sense you got out of there.
On the Samsung A15 you shouldn't worry about space. If you want something really complete and offline, Babbel works well (costs money but sometimes they have promos). If you prefer free with audio, try Memrise which has more speaking content than Duolingo. The truth is no app is going to work miracles in 15 minutes a day, but conversation takes regular practice - really combine the app with subtitles and natural audio, that's where Duolingo really falls short.