Hi,
If you are using an Outlook.com account, please try signing in through Outlook Web on your phone to check if you can send and receive emails. If you are using a non-Microsoft email account, please try sending and receiving emails through its official website.
If you can manage to send and receive emails, please try to clear the cache and data of the Outlook app on your phone.
If the issue persists, please uninstall the app, then restart your device. Install the Outlook app.
If you require further assistance, please don't hesitate to let me know.
Stay Safe!