CallRail activity significantly higher than GA4 event tracking

Hi all - has anyone had this issue before? For example, Aug 5 CallRail has 22 calls logged for that day but our GA4 account only lists 3. I have a pool of 4 numbers, all are being tracked in GTM so it shouldn't matter which number is called as it will be tracked in GA4. What might I be missing here? I'm aware of unique/total volume but the difference from 22 to 3 is a little too big to take that as an answer. 

Thanks!