yesterday i changed my email address from yahoo to gmail and at the time i had steam guard off but when i go to turn it on again there's no option to use an email authenticator, only for mobile

and i have a flip phone which i cant install the steam authenticator app on, it doesnt even have an 'app store'

do i just have to wait a few days to use email, or am i forced to go and buy a i-phone if i want to have steam guard enabled? i really just want to use email for this