Currently it's not possible to send as an alias in the iOS or Android Outlook.
This should be brought into line with OWA and Outlook Desktop
lindalu-MSFT
Microsoft
Aug 09, 2022Hi, we apologize for the confusion where to post your Outlook product feedback. This community was intended to be a temporary location for developers to submit feature suggestions between Microsoft moving off of UserVoice and the release of Microsoft's official Feedback portal app. Now that the latter is released, we encourage you to resubmit this great suggestion on the official Outlook Feedback portal at Outlook · Community (microsoft.com).
Kind regards,
Linda
Microsoft 365 Developer Platform community steward