DO NOT use third-party keyboards while you are using the wallet app!
Somebody has already been robbed because of this. You must only use the stock Android or Apple keyboard, and no others. Better if you uninstall all 3rd party keyboards completely. They collect all data you type on the keyboard at all times, which is a requirement for them to function properly, and there is no telling who is at the other end of the server!
If one doesn't download malicious apps, doesn't visit unknown websites, doesn't connect to public wi-fi, doesn't root smartphone, doesn't install custom ROMs without research and doesn't give unlocked smartphone to friends or strangers, then I think you won't get any problem, especially if you don't own a lot of bitcoins.
For 99% of people: Desktop wallets < Mobile wallets < Hardware wallets