Dear Courtney McNeil
Thank you for posting to Microsoft Community
Based on your description, I understand that you are experiencing a problem with the fonts of emails sent from outlook being out of sync with the fonts on your mobile phone, so please point out if there is a problem with my understanding.
The fonts in the email content are not completely related to the software used. Depending on the device you are using, the fonts in your mailbox may vary. Generally speaking, Microsoft does not recommend users to use files with font format to send and receive emails. Because there is no guarantee that the device receiving emails will also use the font, which may cause your email content to be lost or even the whole paragraph is garbled.
You can click the following link to login to your outlook mailbox and remove the font formatting in the content of your emails through the following settings: gear-shaped [Settings] button in the upper right corner - [Mail] - [Compose and Reply] - [Email Format] change the setting of [Compose Emails Using This Format] to [Plain Text]. Your problem may improve after changing this setting.
Also, have you installed any other customised fonts in your phone? If you don't have a need to use custom fonts on your phone you can try deleting your custom fonts by going to [Fonts] in your phone's settings. It is possible that your phone does not have the same fonts as in the email, so your phone will automatically look for a font that has been determined to be similar under the rules. This substitution may cause the problem you are experiencing.
If you need to use your custom fonts on your phone. Then you may need to seek the help of Apple's professional support staff, as the outlook mobile app does not include font files in all of its features, so we are unable to provide further advice.
For the same reason, you can also try installing the latest Apple update, which will be able to reinstall or supplement your phone's fonts. This may resolve the issue you are experiencing.
This reply may not directly address your issue, so feel free to let me know how it goes any time you reply below.
I look forward to hearing from you!
Carmid.C-MSFT | Microsoft Community Support Specialist