Emails that are not junk are getting sent to the Junk folder. Is there a way to manually mark a sender as safe (Not Junk)? Or is this supposed to happen automatically if you move emails from the Junk folder to your Inbox?
Marking e-mails as junk is done by you e-mail provider (i.e. Google, Microsoft, Yahoo, Fastmail, ...) and not by your phone.
If you manually move e-mails outside the junk folder to your inbox folder for example, the spam engine running on your e-mail provider's servers should, after a time or two, understand that those e-mails are not spam and don't marking them as spam in the future.
Please note that you don't have actual control on this. You would only if the spam filtering would be done on your e-mail client, which is not the case. Usually e-mail providers have on their web mail interface a "mark as not spam" button, but every one is implementing that in different way so there isn't an equivalent button on your e-mail client.