For some reason they make you have a default folder for scheduled emails. You can create a garbage folder if you don't want scheduling and make that folder your default. (I set mine to Missed Conversations for Lync/Skype for Business)
In Outlook on phone, open your inbox and select the settings icon on the top right. Under accounts select your account, if you have multiple accounts. Select Advanced Settings and you will see Scheduled under system folders. Select Scheduled and choose the new garbage folder and ok.
That's all. You will still see Scheduled in your list but non of your emails will be affected.
And here is some info on scheduled emails.