I use yahoo email and need to delete a lot of inbox emails at the same time

Hi all I’m useless with technology but I’ve got an iPhone and a yahoo and iCloud email address but by far the most emails come through yahoo but I access both by using the Mail app on my iPhone. I’ve spent most of the time since November in hospital and I’ve got over 3000 unread emails in my inbox and I would like some ideas on how I can delete emails from certain companies or spam as quickly as possible because I just want to be left with the emails that need a response. But only from my inbox because I have bought things from some companies that send me constant emails and I’ve set up a sub folder for some and I’ve found a way to do it quickly but it would delete all of the emails from that company whether it’s in my sent items or in a sub folder but I just want to delete from my inbox only. Please advise me. Thanks Dav