You’ve stumbled upon one of the many flaws in Airtable which Airtable has so far refused to fix. Sadly, the calendar only displays the primary field value, so you would need to change the primary field value to show you what you need to see in the calendar. You could potentially change it to a formula, if necessary.
Be sure to email email@example.com to let them know how important it is for you to be able to display whatever field you want in the calendar.
@Dinakaran_Rengachary: As Kamille mentioned, if you need to view the calendar within Airtable on a mobile device, you would need to modify your primary field.
Alternatively, a significantly more difficult solution would be to manually craft your own syncing solution to sync your Airtable records (with whatever data you wanted to display) to an external calendar app such as Google Calendar. I’ve done this before for my clients by using Integromat, but it’s relatively complex & tricky to setup.