Salutations CaseyPMacK,
A few questions to help isolate the issue. Can you tell us what happens when using the Search feature within the the Calendar app on your iPhone? Helpful to note if you sync your calendars with any accounts and if there are any error messages, what they say.
Does Siri work when searching the Calendar app? You’d say something like ‘Check my calendar for….<events by title, invitees, location, and notes>.’
Also, let’s make sure those events do still appear on your calendar. Please choose a date you know has an event that isn’t showing in the Search functionality and double verify that it is showing in the Calendar app.
Last setting for right now, in Settings > Siri & Search > Calendar is Show App in Search and Show Content in Search enabled?
Thanks.