I just enabled 2FA and now my email on my smartphone (or other mail client) doesn't work.

once you have enabled 2FA, the regular password will only work for you to use for login to https://webmail.his.com.

It won't work with your other mail applications.
This is usually because the email app in question does not support the 2FA authentication workflow.

Don't worry; this is normal and expected. What you need is to generate an Application Passcode for that specific app/device and use that passcode as your password only for that client.

Follow the instructions in this article:

https://kb.his.com/kb/article/624-Zimbra-2FA-Setting-up-a-new-device-with-2FA