how do I recall an sent email by iphone?

This would be a feature specific for exchange accounts. I have found no indication that iPhones support this feature.

More info about recall:

https://support.office.com/en-us/article/recall-or-replace-an-email-message-that-you-sent-35027f88-d655-4554-b4f8-6c0729a723a0

a relevant question on microsoft community:

https://answers.microsoft.com/en-us/outlook_com/forum/all/how-to-recall-an-email-from-iphone/ca37cb4e-111a-42c8-a804-b22315d9ba62

You can't do it from the phone. You would have to use Outlook directly connected to your Exchange server to try and recall it.