Issues with Native Mail app syncing with work email account which is an office 365 account

My husband has just starting a later model iPhone than he had before, the software is up to date with version ISO 14.4.

Since changing phones he is now having issues with his mailbox syncing properly.

He deletes emails from his work laptop and it doesn’t sync with his phone. They are still sitting there.

Can you please give me some advice, this is very frustrating for him considering he deleted around 50+ emails today and they are still sitting on his phone in the mail app.