My Hotmail works on my iPad but it’s not working on my iPhone. I don’t understand why..

Welcome to the Apple Support Communities.

See: If you can't receive email on your iPhone, iPad, or iPod touch - Apple Support.

If you need more help, I'd contact Microsoft (the owner of Hotmail): Contact a third-party vendor - Apple Support.

Jack

On your iPhone, open Settings ➡️ Mail ➡️ Accounts ➡️ Hotmail: Here check to see whether you have to re-enter the password to your Hotmail account.

Axel F.