Though there are a lot of trading app now available for trading on a phone but i would recommended :
1.Coinbase & Coinbase pro for overall trading.
2.Binance is best for all kinds of altcoins trading.
3. And if you looking for decentralized exchange then Bisq is good option on mobile.
Coinbase was popular since 2017 in the crypto currency market.I had huge experience with coinbase trading platform.Binance is also a best platform for the trading of altcoin. Easily we can exchange available pair of altcoin to bitcoin in a least time period in binance.But I don't have any experience in Bisq platform.And use of laptop to do trading by omitting of mobile.