Trouble Uploading Offline Call Conversions to Google Ads – No GCLID

Hey folks,
I'm trying to upload offline call conversion data to Google Ads, but I keep getting an error saying a required column is missing.

The issue is: I don’t have GCLID since these are call conversions from a phone call form, not ad clicks.

Is there any workaround or alternative identifier I can use (like Call Start Time, Caller Phone Number, etc.)? I’m following Google’s documentation, but it seems focused on GCLID-based uploads.

Anyone successfully done offline call conversion tracking without GCLID? Would love any insights or tips. Thanks in advance!