Just check what you want to download very carefully. The Poloniex exchange for example for a long time didn't have an official application and people often downloaded the application from scammers.
First, choose the exchange on which you will trade. Then read the general security basics related to the phone and the security of working on the exchange (protection of the mailing address, 2fa, etc.). There are various topics in this section - check out. And never put unnecessary applications - all sorts of trading bots, market monitors and the like - all this is unnecessary and can lead to losses. You need an application from the exchange for trading and an application for 2fa. Or sometimes you can trade through the web browser interface.