@Scott Barber Welcome to Microsoft Q&A forums.
Unfortunately, it is currently not possible to use a custom port for Azure Database for MySQL server. The default port is 3306.
However, if you have a requirement to a specific major version of MySQL, you can use port 3308 for v5.7 clients and port 3309 for v8.0 client
Read more here
----------
If an answer is helpful, please click on or upvote which might help other community members reading this thread.