Hi Denise,
As of now, the options for Outlook Calendar Notifications(Sound) is very limited. There's no option yet to set or customize the notifications to be louder and longer using the Outlook application for iOS. Same goes with the option to notify continuously until someone shuts it off. Here are some screenshots of the options under Calendar Notifications:
You can only choose which notification sound you're going to use.
On the other hand, have you tried contacting your device manufacturer to see if there are settings on your device that can make the notifications for Outlook Calendar to be louder and longer? If not yet, you can give it a try.
You can also recommend to have a feature added or modified in the future by sending a feedback. You can post this in Outlook UserVoice forums so that our developers can look into implementing it for you.
In Outlook UserVoice forums, there are thousands of other users that can upvote it and it will provide our engineers better visibility on feedback that our consumers are experiencing with our products. You can post this here.
Feedback items regularly receive Microsoft responses on the submissions so you can see what we are doing about your feedback. Please revisit frequently to see the status of your feedback items.
Should you have any other concerns, don’t hesitate to let us know.
