Outlook won't junk emails from a couple of senders

Is it an Outlook.com or work account? Then add them under Blocked senders in Outlook on the web as well (Settings > Mail > Junk email). That's done on the server, so it catches them even when desktop Outlook is closed, and the phone app follows it.

Check your Safe Senders list first. If those addresses (or their whole domain) are on it, or they're saved in your contacts with "also trust email from my contacts" ticked, Outlook will never junk them, whatever the filter thinks. Once they're off that list, right-click one of the emails, Junk, Block sender. If they keep changing the address, block the domain instead. And look at your inbox rules too. A rule that moves mail into a folder runs before junk filtering, so an old rule can pull them straight past it.