anything that is not a clean and encrypted cold storage is susceptible to be hacked, stolen, lost specially if it is your phone which you carry around with you!!!

in fact putting your bitcoins on your phone or things similar to that is like carrying all your money in a bag over your shoulder. would you do that? of course not. you put your money in a safe place with a bank, a safety deposit box or in your mattress and only carry around pocket change with you.