Dear Rachel Sollis
Thanks for your post in Microsoft Community.
I understand the confusion that you don't have access to your email at the moment.
According to your description, your current predicament is due to the fact that your current setup doesn't conform to the modern authentication methods that Microsoft has recently rolled out.
What is modern authentication?
Modern authentication is a security protocol that provides stronger security protections, including multi-factor authentication (MFA) and conditional access. Microsoft encourages users to migrate from the old Basic Authentication to Modern Authentication to improve the security of their accounts.
The following is an official description from Microsoft. You can refer to it and confirm if you find yourself in the following situation:
Modern Authentication Methods now needed to continue syncing Outlook Email in non-Microsoft email apps - Microsoft Support
Since you are using the Mail app that comes with your iPhone, you can refer to the following steps:

It is hoped that the above recommendations will provide you with help. Please do not hesitate to contact us if you have any further concerns or questions.
Best Regards
Clara G| Microsoft Community Support Specialist