The suggested addresses are derived from all the messages in your mailbox. If you received junk mail from your own address, a tactic spammers often use to prevent you from blocking the sending address, the suggestions may just be from the junk messages. Since you are using Outlook for iOS, are you synching your contacts between iOS and Outlook.com? If you are, try logging into https://outlook.live.com/, staring a new message and performing the same thing you're doing in Outlook for iOS. If that same entry appears, move the mouse over it. You should see an X appear to the right of the name. Click that to remove suggestion. Now, return to Outlook for iOS to see if that corrects the behavior. If not, write back.
Here is Microsoft's guide to removing suggested recipients: https://support.microsoft.com/office/dbe46e31-c098-4881-8cf7-66b037bce23e