How do I send from another email address through outlook.com on iphone?

When logged into outlook.com on my computer I can choose the from address to be from one of my other emails, such as gmail. I cannot find this same option when using my iphone, unless i log into outlook.com website. It does not appear to be an option when accessing through the mail app. Any ideas? I would like to delete all my other accounts from my phone since I have my messages forwarded to this outlook.com email, but i need to be able to send using the other addresses.