How do I mark unwanted emails as spam on my iPhone?
If you get an unwanted email in your Gmail inbox, you can block or unsubscribe from the sender or report the message in Gmail. Alternatively, you can use mail rules to block email from iCloud Mail. You can connect Gmail, Yahoo Mail, and other service providers on iPhone and iPad and block in the mail app itself. If you're not too keen on blocking senders, you can simply move unwanted emails to the spam folder in the standard Mail app, and then mark those emails as spam on your iPhone or iPad - https://emailspedia.com/how-to-block-email-on-your-iphone/