It occurs to me that you're doing things the hard way! Perhaps a little bit of history might help to explain why I'm thinking that:
In the early days of the internet web-browsing and email were two entirely separate things. You used a web browser (which would have been Internet Explorer for most people then) to visit websites and an email client to access your emails. (For most home users that client would have been Outlook Express, with most office users relying on the full Outlook program). You couldn't access your email via your web browser even if you wanted to; it simply wasn't possible.
Then along came web-based email services, which allowed people to access their email from any computer (instead of just their home or office one) by logging in from a web broswer. However that way of getting to your email service (i.e. via a web browser) has always been only 'second best'. You won't find any big businesses using web browsers to send and receive email; they all still use a dedicated email client. Such programs offer greatly flexibility (e.g. when searching for content within emails).
Now let's fast forward to the days of smart phones. One of the great things about them is that people have now remembered that the best way to use email is via a dedicated program ( = app), rather than by using a web browser. So you really ought to be using either the email app that came with your phone or, indeed, any other dedicated app. Then . . .
(a) all of your email accounts can be brought together in one place ;
(b) you'll be permanently logged in (so you won't have to bother with a log in procedure) ; and
(c) you'll be alerted to incoming emails as soon as they've been sent, with no need to keep checking your mail.
The email app that came with your phone is perfectly good enough for the job but, since you're using Yahoo Mail, you might also want to consider using Yahoo's own email app:
https://play.google.com/store/apps/details?id=com.yahoo.mobile.client.android.mail&hl=en_GB